Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

Treasury Secretary Janet Yellen will hold a bilateral meeting with Ukrainian Prime Minister Denys Shmyhal in Washington, D.C., on Thursday, a Treasury Department spokesperson confirmed. Ukraine's finance minister will also attend.

The meeting will take place during the annual conferences of the International Monetary Fund and the World Bank. The conferences draw leaders from the G20, of which Russia is currently a member.

While Yellen will participate in some meetings and panels where Russian officials will be present, she will skip others, a Treasury Department official said.

-ABC News' Sarah Kolinovsky

Tennis players from Russia and Belarus have been banned from this summer's Wimbledon Championships due to the "unjustified and unprecedented military aggression" in Ukraine, The All England Lawn Tennis Club said.

"It would be unacceptable for the Russian regime to derive any benefits from the involvement of Russian or Belarusian players," the statement said, adding: "If circumstances change materially between now and June, we will consider and respond accordingly."

Over 5 million people have now fled Ukraine, according to the United Nations High Commissioner for Refugees.

The majority of those refugees -- over 2.8 million -- are in Poland.

Russia’s military issued another ultimatum on Wednesday, calling for Ukrainian forces to lay down their arms and leave a Mariupol steel plant, according to Russian state media.

Moscow claimed that Ukrainian troops and civilians would be allowed to leave the Azovstal Iron and Steel Works plant without harm during a cease-fire beginning at 2 p.m. local time.

Ukrainian forces at the besieged plant rejected a similar offer on Tuesday.

More than 1,000 civilians are sheltering on the grounds of the sprawling industrial plant, the Mariupol City Council said on Monday.

A Russian official, Dmitry Polyansky, on Tuesday accused Ukrainian troops of using civilians at the plant as human shields.

“One month into the siege of Azovstal plant, those same radicals and neo-Nazis suddenly declared that allegedly there had been civilians inside the plant all that time, even though until yesterday, they had never uttered a word about it," Polyansky told the U.N. Security Council during a session on Ukraine on Tuesday.