Russia claimed Wednesday that more than a thousand Ukrainian soldiers had surrendered in Mariupol, a besieged port city in southeastern Ukraine that is still held by Ukrainian forces.

"In Mariupol city, near the 'Illich' Steelworks, 1,026 Ukrainian servicemen of the 36th Marine Brigade have voluntarily laid down their arms and surrendered as a result of a successful offensive by the Russian Armed Forces and Donetsk People's Republic militia units," the Russian Ministry of Defense said in a statement.

The surrendering troops included 162 officers and 47 women, according to the ministry.

"151 wounded Ukrainian servicemen of the 36th Marine Brigade received primary medical care immediately on the spot, after that they were all taken to the Mariupol city hospital for further treatment," the ministry added.

The Biden administration could announce as early as Wednesday upward of $750 million in additional military assistance to Ukraine, a U.S. official told ABC News.

The new assistance could possibly include a range of military hardware -- including howitzers, artillery and Humvees -- though the full package still needs to be finalized, the official said.

-ABC News' Luis Martinez

Correction: Mi-17 helicopters are not being considered as part of the package, as previously reported.

President Joe Biden used the word "genocide" for the first time to describe Russia's actions in Ukraine during remarks on Tuesday.

"Your family budget, your ability to fill up your tank -- none of it should on hinge on whether a dictator declares war and commits genocide half a world away," Biden said in Menlo, Iowa, during remarks primarily about the U.S. economy.

Biden was asked by reporters on April 4 if he thought the atrocities in Bucha were a genocide, as Ukrainian President Volodymyr Zelenskyy had claimed. "No, I think it is a war crime," Biden responded then.

That same day, Biden's national security adviser, Jake Sullivan, said the administration had not yet seen the "systematic deprivation of life" necessary to meet the definition of genocide.

Biden confirmed his word choice to the White House pool Tuesday evening before boarding Air Force One, saying that since last week the "evidence is mounting."

"Yes, I called it genocide," Biden said. "Because it has become clearer and clearer that Putin is just trying to wipe out the idea of even being able to be a Ukrainian."

He then qualified that the determination of genocide is officially up to legal experts, but that "it sure seems that way to me."

-ABC News' Sarah Kolinovsky

The U.S. State Department is condemning the arrest in Russia of Vladimir Kara-Murza, a Russian opposition activist and critic of the Kremlin's invasion of Ukraine.

State Department spokesperson Ned Price said Kara-Murza's arrest on Monday is another example of a Russian government "that is more aggressive beyond its borders and more oppressive within its borders."

He condemned Kara-Murza's arrest, noting that the activist has previously been arrested by Russian authorities and that he has survived two poisoning incidents.

"The Russian people -- and this is the key point -- like people everywhere, have the right to speak freely, to form peaceful associations, to exercise their freedom of expression and to have their voices heard through free and fair elections," Price said.

Kara-Murza, a Washington Post columnist who has testified before Congress, survived poisoning incidents in 2015 and in 2017. At the time of his second poisoning, Kara-Murza's wife, Evgenia Kara-Murza, gave an exclusive interview to ABC News in which she pleaded for then-President Donald Trump to support her husband and warned that Putin "cannot be dealt with on friendly terms."

Following her husband's arrest this week, Evgenia Kara-Murza posted a message on Twitter calling attention to her husband's arrest.

"Twice have the Russian authorities tried to kill my husband for advocating for sanctions against thieves and murderers, and now they want to throw him in prison for calling their bloody war a WAR. I demand my husband's immediate release!" Evgenia Kara-Murza, who lives in the Washington, D.C., area, tweeted.

-ABC News' Conor Finnegan

At least one person -- a journalist -- was killed in a rocket attack on a residential building in Kyiv on Thursday evening, ABC News has learned.

Kyiv Mayor Vitali Kilitschko said Friday that rescuers had found the body of a victim amid the rubble.

Radio Liberty, a service of the U.S.-funded Radio Free Europe/Radio Liberty, reported that one of its employees, Vira Gyrych, was killed when a Russian missile hit her apartment in the Ukrainian capital on Thursday. Her body was found beneath the wreckage Friday morning, according to the report.

Gyrych had worked as a journalist and producer for Radio Liberty's Kyiv bureau since 2018. Prior to that, she worked for leading Ukrainian television channels, according to Radio Liberty.

"The editorial staff of Radio Liberty expresses its condolences to the family of Vira Gyrych and will remember her as a bright and kind person, a true professional," Radio Liberty said in its report.

Israeli Ambassador to Ukraine Michael Brodsky also confirmed Gyrych's death in a Twitter post, saying she was a former employee of the Israeli embassy in Kyiv.

Thursday's rocket attack came as United Nations Secretary-General Antonio Guterres visited Kyiv. Five Russian missiles flew into the city, according to Ukrainian President Volodymyr Zelenskyy. At least 10 people were injured, including four who were hospitalized, according to the Kyiv City Council.