The city of Al-Qa'im on the Iraqi border with Syria as well as other areas along the Iraqi border with Syria "are being subjected to air strikes by United States aircraft," the spokesperson for the commander-in-chief of the Iraqi Armed Forces said in a statement.

"These strikes constitute a violation of Iraqi sovereignty, an undermining of the efforts of the Iraqi government, and a threat that will drag Iraq and the region into unforeseen consequences, the consequences of which will be disastrous for security and stability in Iraq and the region," the statement continued.

Defense Secretary Lloyd Austin said U.S. military forces, at Biden's direction, conducted strikes on seven facilities inside Iraq and Syria that "Iran’s Islamic Revolutionary Guard Corps (IRGC) and affiliated militias use to attack U.S. forces."

"This is the start of our response," Austin said in a statement. "The President has directed additional actions to hold the IRGC and affiliated militias accountable for their attacks on U.S. and Coalition Forces. These will unfold at times and places of our choosing."

Like Biden, Austin stressed the U.S. doesn't seek conflict in the Middle East but attacks on U.S. troops won't go unanswered.

"We will take all necessary actions to defend the United States, our forces, and our interests," he concluded.

President Biden, who earlier Friday attended the dignified return of the three Army reservists killed in the Jordan drone attack, signaled more action is to come.

"Our response began today," Biden said in his first statement on the strikes in Iraq and Syria.

"This afternoon, at my direction, U.S. military forces struck targets at facilities in Iraq and Syria that the IRGC and affiliated militia use to attack U.S. forces," he added. "It will continue at times and places of our choosing."

He ended saying, "The United States does not seek conflict in the Middle East or anywhere else in the world," he continued. "But let all those who might seek to do us harm know this: If you harm an American, we will respond."

President Biden is facing a turning point in the Middle East conflict that carries significant risks of escalation and heavy election-year political consequences.

The debate inside the White House ahead of the retaliatory strikes was tense, according to a U.S. official, as the administration weighed options that some believe will send a clear message to Iran-backed proxy groups to stop the attacks and others fear could trigger broader fighting in the region.

"The choices that any administration and every administration have faced since the Iranian Revolution are fraught," Aaron David Miller, a former State Department official, told ABC News. "They are not between good and bad policies. They're between bad and worse policies."

Biden's decision making is made only more complicated by the impending election, they said. Many Republicans, including Donald Trump, have accused him of being weak in his response to Iran-backed groups and their attacks on U.S. forces.

"He's in a politically tough spot because policy would compel him to think about this and act with a scalpel," the Center for a New American Security's Jonathan Lord said. "But this being an election this year, and this being probably the premier foreign policy issue Republicans are lining up to cudgel him with, he can't let policy be the only consideration here. Politics, of course, plays a role."

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The Department of Defense is in the early stages of battle damage assessment "but we believe that the strikes were successful," National Security Council spokesperson John Kirby told reporters in a call Friday.

"The initial indications are that we hit exactly what we meant to hit, with a number of secondary explosions associated with the ammunition and logistics locations," Lt. Gen. Douglas Sims, the director of the Joint Chiefs, said on the call.

Kirby said the strikes took place in the course of 30 minutes and involved over 125 precision-guided munitions. Of the seven total strike locations, three were in Iraq and four were in Syria, according to Sims.

Targeted facilities included command and control centers, intelligence centers, rocket missile and drone storage facilities, and logistics ammunition supply chain facilities, Kirby said.

Kirby noted the targets were chosen to avoid civilian casualties and because they were connected to enabling the attacks against the U.S. service members.

The administration does not know at this time if or how many militants may have been killed or wounded.

Officials would not tell ABC News Chief White House Correspondent Mary Bruce definitively whether there will be more strikes Friday night but said all U.S. aircraft were out of harm's way.

Kirby said the strikes are expected to continue in the "coming days."

-ABC News' Fritz Farrow, Sarah Kolinovsky and Molly Nagle