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

Ukraine accused Russia of conducting state-sponsored kidnapping of children, Ukrainian Foreign Minister Dmytro Kuleba said in a statement to the United Nations Security Council on Friday.

"The magnitude of the humanitarian crisis brought on by Russia's aggression against Ukraine cannot be overstated. I would like to highlight here one of numerous horrendous facts - Russia is now implementing in Ukraine probably the largest instance of state sponsored kidnapping of children in history of our modern world," Kuleba said.

-ABC News' Ellie Kaufman