-- Two Syrian jets on Friday took off from the air base that was hit by U.S. missiles and carried out strikes on areas under ISIS control in the countryside of eastern Homs province, according to the Syrian Observatory for Human Rights.
The Syrian government responded to Thursday night's U.S. aistrike on its Shayrat Air Base in Homs province by quickly fixing the base and allowing the two planes to take off from there, the human rights organization said.
A U.S. official said Syrian planes took off from the airfield Friday but did not confirm the airstrikes.
The official noted that as many as 20 Syrian aircraft were destroyed in Thursday's airstrikes but added that the missiles did not target every aircraft at the base and that the runway was untouched.
The departures came after U.S. ambassador to the United Nations, Nikki Haley, warned that the United States is "prepared to do more" in Syria, one day after U.S. warships fired a barrage of cruise missiles at the Syrian government air base.
"The United States took a very measured step last night. We are prepared to do more, but we hope that will not be necessary," Haley said Friday during a special open session of the U.N. Security Council devoted to discussing Syria.
The United States launched the direct assault against Syrian President Bashar al-Assad's regime in response to a chemical weapons attack earlier this week that killed dozens of civilians in northern Syria.
Haley accused Assad's regime of carrying out Tuesday's horrific attack in Idlib province, saying this "fully justified" the U.S. government's decision to strike the Syrian air base.
"The moral stain of the Assad regime could no longer go unanswered," she said.
"The intent here wasn’t just to punish; it was deter future use," retired Vice Adm. Robert Harward, an ABC News contributor and the former deputy commander of U.S. Central Command who turned down the role of national security adviser after Michael Flynn's resignation, told ABC's "Good Morning America" on Friday.
The Shayrat Air Base has been one of Russia's main airfields in Syria, serving as a forward operating base for Russian attack helicopters to support Assad regime offensives in Homs province amid Syria's ongoing conflict.
U.S. Secretary of State Rex Tillerson said the United States did not discuss the military strike with Russian President Vladimir Putin or political leadership in Moscow either before or after it occurred. But the U.S. military said it communicated with its Russian counterpart to minimize any chance of Russian causalities, particularly any Russians operating out of the targeted air base.
U.S. President Donald Trump, who blamed Syria's leader for the latest chemical weapons attack, said on Thursday night that the airstrikes were in the "vital national security interest" of the United States.
A senior U.S. military official said the 59 missiles reached their intended targets, and approximately 20 aircraft were struck. The official also said that there were no Russian aircraft at the base at the time, nor was there any indication that Syria had detected incoming missiles before they struck.
According to Pentagon spokesman Capt. Jeff Davis, the missiles targeted aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defense systems and radars.
The time of the airstrike was chosen to minimize civilian casualties, Davis said.
The Shayrat Air Base housed chemical weapons prior to 2013 but it is unclear if weapons are still stored at the facility.
A U.S. official told ABC News the missiles did not target any suspected chemical weapons stockpiles at the air base because that was not the intent of the operation.
In an interview Friday on ABC's "Good Morning America," Col. Steve Ganyard, an ABC News contributor and a retired Marine Corps fighter pilot who served as former deputy assistant secretary of state in the Bureau of Political-Military Affair, said that "the message has been sent."
"We'll just have to see how Assad reacts to this," Ganyard added.
The Syrian government swiftly denounced what it described as "illegal action targeting one of our air bases against our sovereignty," the first time the U.S. military intentionally targeted Assad's forces since the beginning of Syria's ongoing civil war.
The Syrian president's office said in a statement Friday that the United States "naively followed a false and lying propaganda campaign" that led it to "carry out this irresponsible recklessness."
“The presidency of the Arab Syrian republic asserts that what America carried out was an irresponsible act that only reflects short-sightedness, a narrow perspective and political and military blindness toward reality," the statement said. “The fact that the United States of America has committed this shameful act by targeting an airport of a sovereign state clearly demonstrates, once again, what Syria has said and continues to say –- that changing administrations doesn’t change the deep policies of this government, namely, the targeting of countries, the subjugation of people and an attempt to dominate the world."
The Syrian army delivered a statement on state-run television on Friday, saying six people were killed in the U.S. airstrikes. The Syrian army went on to describe the United States as "the initiators of the ongoing dirty war against our people."
According to the Britain-based Syrian Observatory for Human Rights, the death toll has increased to eight.
Russia, a staunch ally of the Syrian government, also had harsh words for the United States, calling the military airstrike a "clear act of aggression" that would "further undermine Russo-American relations."
The presence of military personnel from the U.S. and other countries in Syria without the permission of the government "or a resolution of the U.N. Security Council is a gross, clear and in no way justified violation of international law," the Russian foreign ministry said in a statement Friday. "If before it was explained as a mission in the battle against terrorism, now it is a clear act of aggression against a sovereign Syria. The taking of these actions by the U.S. today yet further undermines Russo-American relations."
The Russian foreign ministry said it was calling for an urgent U.N. Security Council meeting and that Moscow was suspending its current memorandum of understanding with the U.S. military that was aimed at avoiding air collisions in Syria.
Both Russia and the United States have a large air presence in Syria and had established so-called "de-confliction" channels to avoid collisions of their respective aircraft.
The Russian foreign ministry also suggested that the U.S. decision to strike the Syrian regime was made in advance of Tuesday's chemical weapons attack, calling it "a pretext for a demonstration of force."
The Russian defense ministry claimed only 23 U.S. missiles hit the Syrian air base, saying it's unclear where the others landed. The airstrikes destroyed a supply dump, a training building, the canteen, six planes that were under repair in hangars and a radar station. The ministry claimed the runways and operational Syrian aircraft were not damaged.
Citing the Syrian military, the Russian defense ministry said four Syrian soldiers were killed and six suffered burns while putting out fires caused by the explosion. Two Syrian soldiers remain unaccounted for.
"As such, the military effectiveness of the American massed missile strike on the Syrian airbase was extremely low," the Russian defense ministry said in a statement Friday.
What prompted the U.S. to strike?
At least 87 civilians, including 31 children and 20 women, have died from a chemical weapons attack in the Syrian town of Khan Sheikhoun in Idlib province on Tuesday, according to the Syrian Observatory for Human Rights.
Harrowing footage from the scene showed victims gasping for air and being hosed off, as well as the lifeless faces of those who didn’t survive. It's the worst chemical attack the war-torn country has witnessed since 2013.
Trump on Wednesday firmly condemned the "heinous actions" in Syria, telling reporters that the attack "crossed a lot of lines for me."
"I do change, and I am flexible, and I'm proud of that flexibility. And I will tell you that attack on children yesterday had a big impact on me," the U.S. president said during a press conference at the White House with Jordan's King Abdullah II. "It's already happened, that my attitude towards Syria and Assad has changed very much."
After conducting autopsies on victims who were brought to Turkish hospitals for treatment, Turkey's health ministry confirmed Thursday that the patients had been exposed to sarin gas, a banned nerve agent.
A U.S. official also said the symptoms exhibited by the victims pointed to sarin gas.
The U.S. official told ABC News that a Syrian military fixed-wing aircraft dropped the chemical weapons on what was an underground hospital in the town run by an al-Qaeda affiliated rebel group formerly known as Al-Nusra Front.
Syrian Foreign Minister Walid Moallem firmly denied that his government used chemical weapons in Tuesday's deadly attack. He told reporters at a televised press conference in the capital of Damascus on Thursday that "the Syrian Arab Army has never used chemical weapons and will not use chemical weapons against Syrians and even against terrorists."
Moallem said rebels linked to al-Qaeda and ISIS have brought chemicals from Iraq and Turkey into the country and have been stockpiling them in residential areas.
On Wednesday, Russia's Defense Ministry blamed Syrian rebels for the attack, saying that the Syrian air force struck a warehouse where opposition militants were storing chemical weapons — a statement that contradicts testimony from residents, doctors and activists on the ground.
Syria's ongoing conflict
Tuesday's chemical weapons attack is the latest atrocity in Syria's ruinous six-year war.
What started as a local protest movement in Syria’s southern city of Dara'a expanded into a full-fledged civil war by 2012. ISIS, which grew out of al-Qaeda in Iraq, took root in northern and eastern Syria in 2013 after seizing swaths of territory in neighboring Iraq. The jihadist group is fighting to overthrow Assad's regime and establish a caliphate.
The Syrian Civil War has pulled in the United States, Russia, Iran and almost all of Syria's neighbors. It has become the largest humanitarian crisis since World War II, according to the U.N.
In an administration briefing to the Senate on Friday, Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, did not elaborate on any long-term plans or strategy the administration has for Syria, according to members in the briefing.
"There's not a plan of further engagement right now," Sen. Bob Corker, R-Tenn., the chairman of the Senate Foreign Relations Committee, told reporters. "This was a very surgical response to chemical weapons use."
Rep. Eliot Engel, D-N.Y., the top Democrat on the House Foreign Affairs Committee, said of the briefing, "It was fuzzy in terms of where do we go from here. Essentially, the vice president's going to be contacting Congress within the next few days, give us an indication of where their heads are at [in the White House]."
While many lawmakers argued that the airstrikes were covered by previous war authorizations, Sen. Rand Paul, R-Ky., wants Congress to consider a new authorization for the use of military force after the Easter recess.
"We should have a huge constitutional debate as well as the debate over war," he said today. "No serious person believes most of the wars that we’re now involved with had anything to do with 9/11."
From Trump’s Mar-a-Lago estate in Florida, Treasury Secretary Steven Mnuchin today said additional sanctions will be imposed against Syria "in the near future," calling the sanctions a "very important tool" to stop "this sort of activity."
Haley, who is acting as the president of the U.N. Security Council for the month of April, denied a request from Bolivia for a closed session on Syria, insisting that "any country that chooses to defend the atrocities of the Syrian regime will have to do so in full public view.”
During Friday's U.N. Security Council open session, Russian deputy ambassador to the United Nations, Vladimir Safronkov, condemned the "illegitimate" U.S. military action on the Syrian air base, calling it a "flagrant violation" of international law. Safronkov called on the United States to instead "work together" with Syria and Russia to combat terrorism in the country.
"We call on the United States to immediately cease its aggression," Safronkov said.
Haley spoke next, and she didn't mince words in rebuking those who support Assad's regime.
"Every time Assad has crossed the line of human decency, Russia has stood beside him," Haley said. "The world is waiting for the Russian government to act responsibly in Syria."
She also suggested that Russia may have known about Syria's illicit chemical weapons supply and may have even had a hand in Tuesday's attack.
"Russia's supposed to be a guarantor of the removal of chemical weapons from Syria. Think about that," Haley said. "Russia is supposed to have removed all the chemical weapons from Syria. But obviously that has not happened."
She continued, "As innocent Syrians continue to be murdered in chemical attacks, let's think about the possible reasons for Russia's failure. It could be that Russia is knowingly allowing chemical weapons to remain in Syria. It could be that Russia has been incompetent in its efforts to remove the chemical weapons. Or it could be that the Assad regime is playing the Russians for fools."
Syrian ambassador to the United Nations, Bashar Jaafari, said the United States acted "illegally against the Syrian Arab Army" and "without genuine knowledge of what happened" in the chemical weapons attack, or "without identifying who was responsible."
Jaafari added that U.S. airstrikes harm counterterrorism efforts.
ABC News' Benjamin Gittleson, Luis Martinez, Alexander Marquardt, Alexander Mallin, Kirit Radia, Patrick Reevell, Joseph Simonetti, Daniel Trefcer and Marcus Wilford contributed to this report