Ukrainian President Volodymyr Zelenskyy told reporters that U.S. Secretary of State Antony Blinken and Defense Secretary Lloyd Austin will visit Ukraine on Sunday.

Zelenskyy said they will discuss the list of weapons Ukraine needs and their delivery date.

A spokesperson for the State Department declined to comment and a spokesperson for the Defense Department said they had "nothing to offer" on the trip.

-ABC News' Jason Volack

British Prime Minister Boris Johnson told Ukrainian President Volodymyr Zelenskyy that Russia would be held to account for its actions and that the British government is helping collect evidence of war crimes, when the two spoke on Saturday.

Johnson confirmed that the U.K. will provide Ukraine with more defensive military aid including protected mobility vehicles, drones and anti-tank weapons.

He also updated Zelenskyy on new U.K. sanctions against members of the Russian military and confirmed the U.K. would reopen its embassy in Kyiv next week.

Ahead of the U.N. Secretary-General’s meetings with Zelenskyy and Russian President Vladimir Putin, both leaders agreed on the importance of establishing a cease-fire and humanitarian corridor to allow civilians to leave Mariupol, according to a statement from the British government.

The leaders discussed the U.K.'s efforts with partners to reach a long-term security solution for Ukraine, including discussions with international partners to provide more financial support to Ukraine.

Russian forces attacked a steel plant in the shattered Ukrainian port city of Mariupol on Saturday, according to Oleksiy Arestovich, an adviser to the Ukrainian president's office.

In a briefing, Arestovich said Russian forces had resumed airstrikes on the plant and were trying to storm it, a reversal of Russian President Vladimir Putin's order two days earlier.

Ukrainian officials estimate that about 1,000 civilians are sheltered in the plant along with the remaining Ukrainian fighters.

Busses promised by Russia to evacuate people from Mariupol did not arrive on Saturday.

At least 200 Mariupol residents had gathered near the Port City shopping center to be evacuated to Zaporizhia, adviser to the mayor of Mariupol Petro Andryushchenko said on Facebook.

“Instead of the buses promised by the Russian side, the Russian military approached Mariupol residents and ordered them to go away because "there will be shelling now." In fact, with rough coercion, they dispersed people. The buses were not submitted for loading,” he wrote.

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.