At least six civilians were killed and eight others were injured Sunday when Russian missiles slammed into houses and apartment buildings in an eastern Ukrainian city, Ukrainian officials said.

The attack occurred in downtown Kostiantynivka, a city in the Donetsk region of eastern Ukraine, the site of the war’s fiercest fighting.

Andriy Yermak, deputy head of the Ukrainian Presidential Office, said at least six people were killed in the attack.

Three Russian S-300 long-range missiles and four other rockets hit homes and apartment buildings in Kostiantynivka, according to Pavlo Kyrylenko, the regional governor.

Kostiantynivka is about eight miles west of the embattled town of Bakhmut, currently the main hotspot of the war.

-ABC News' Tatiana Rymarenko

U.S. Secretary of State Antony Blinken urged the Kremlin to release imprisoned Wall Street Journal reporter Evan Gershkovich in a phone call Sunday with his Russian counterpart, according to a State Department spokesperson.

Blinken spoke with Russian Foreign Minister Sergey Lavrov, conveying the United States' "grave concern" over the "unacceptable detention" of a U.S. citizen, according to Vedant Patel, a deputy spokesperson for the State Department.

"The secretary called for his immediate release. Secretary Blinken further urged the Kremlin to immediately release wrongfully detained U.S. citizen Paul Whelan," said Patel, referring to the American held in Russia on espionage charges since 2018.

According to a read out of the phone call released by the Kremlin, Lavrov emphasized that Gershkovich "was taken red-handed while trying to obtain classified information, collecting data constituting a state secret under the guise of journalistic status."

"In the light of the established facts of illegal activity of a U.S. citizen, of whose detention the U.S. Embassy in Moscow was notified in accordance with the established procedure, his further fate will be determined by the court," the Kremlin said in a statement.

The Kremlin said that during the conversation, Lavrov emphasized officials in Washington and the Western media are "escalating the hype with the clear intention of giving this case a political coloring."

Blinken and Lavrov also spoke of the "importance of creating an environment that permits diplomatic missions to carry out their work," according to Patel.

More than three dozen of the world’s top news media organizations are calling on Russia to release Wall Street Journal reporter Evan Gershkovich.

The news groups joined the Wall Street Journal and the Committee to Protect Journalists, in penning a letter to Anatoly Antonov, Russia’s ambassador to the United States, writing Gershkovich's "is a journalist, not a spy." The media organizations -- including the Associated Press, New York Times, the Washington Post and The Times of London -- wrote that Kershkovich's "unwarranted and unjust arrest" represents "a significant escalation" of anti-press actions by the Russian government.

"Russia is sending the message that journalism within your borders is criminalized and that foreign correspondents seeking to report from Russia do not enjoy the benefits of the rule of law," the letter reads.

The media groups urged Russia to immediately give Gershkovich access to a lawyer hired by the Wall Street Journal and allow him to communicate with his family.

The Kremlin has yet to publicly respond to the letter.

-ABC News' Patrick Reevell

Belarusian President Alexander Lukashenko warned that Russian strategic nuclear weapons could be deployed in his country, according to The Associated Press.

Earlier this week, Russian President Vladimir Putin announced Russia intended to deploy tactical, comparatively short-range and small-yield nuclear weapons in Belarus.

Russia's Permanent Representative to the United Nations Vasily Nebenzya told the Security Council that the decision to deploy nuclear weapons in Belarus does not violate international obligations. Nebenzya added that Russia has repeatedly called on the U.S. to return all its nuclear arsenals from Europe to U.S. territory.

"Russian President Vladimir Putin directly pointed out that we are not transferring nuclear weapons. We are talking about the transfer of the Iskander-M operational-tactical missile system to the Republic of Belarus, the re-equipment of aircraft of the Belarusian Air Force and the training of crews, the construction of a special storage facility for tactical nuclear weapons at territory of Belarus," Nebenzya said.

-ABC News' Will Gretsky

The United States announced an additional $2 billion military aid package for Ukraine on Friday, as the Eastern European country marks the one-year anniversary of Russia's full-scale invasion.

The new aid package includes more missiles for Ukraine's U.S.-supplied High Mobility Artillery Rocket Systems (HIMARS), additional 155mm artillery ammunition, more Switchblade one-way drones and other military equipment, according to the U.S. Department of Defense.

"One year into a war of aggression waged by a permanent member of the U.N. Security Council, our allies and partners worldwide stand united and resolute," U.S. Secretary of Defense Lloyd Austin said in a statement. "Putin's reckless, illegal war is not just an all-out assault on Ukraine's sovereignty and a historic threat to European security. It is also a direct attack on the system of rules, institutions, and laws that the world built at such great cost after World War II -- a system that rejects aggression and respects the rights of all countries, big and small."

The additional aid is being provided under the Ukraine Security Assistance Initiative (USAI) plan, meaning this equipment and artillery have to be made from scratch before being delivered, which will take time. This is different from the other aid packages that come from existing U.S. military stockpiles and get delivered faster.

With the new aid package, the Biden administration has now provided $31.8 billion in assistance to Ukraine since Russia's war began on Feb. 24, 2022.

"Putin thought that Ukraine’s defenses would collapse, that America's resolve would falter, and that the world would look the other way. He was wrong," Lloyd said. "One year later, Ukraine's brave defenders have not wavered, and neither has our commitment to support them for as long as it takes. Despite the Kremlin's campaign of cruelty, the people of Ukraine have shown stunning bravery, skill, and fortitude. Today and every day, we stand by the courageous Ukrainians fighting to defend their country, and we mourn with those who have lost their loved ones in Moscow's monstrous and unnecessary war."

"Difficult times may lie ahead, but let us remain clear-eyed about what is at stake in Ukraine," he added. "And let us remain united in purpose and in action -- and steadfast in our commitment to ensure that a world of rules and rights is not replaced by one of tyranny and turmoil."

-ABC News' Luis Martinez