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

Russian President Vladimir Putin canceled his military's attack on a Mariupol steel plant, one of the last areas in the port city held by Ukrainian forces, ordering his troops to instead seal all exit routes from the sprawling plant.

“I consider the proposed assault on the industrial zone impractical,” Putin told Sergei Shoigu, his defense minister, during a meeting televised on Thursday by Russian state media, according to a translation of the Kremlin’s official transcript.

The Mariupol city council claimed Tuesday that there are at least 1,000 civilians, mostly women with children and the elderly, seeking shelter in the Azovstal Steel and Iron Works plant. It was unclear how many Ukrainian troops were defending the site.

Putin in the televised meeting ordered his troops to “block” the industrial zone. He repeated the claim that Moscow would let troops leave unharmed if they lay down their weapons and surrender.

“There is no need to climb into these catacombs and crawl underground on these industrial facilities," Putin said. "Block this industrial area so that the fly does not fly."

During a G20 meeting of economic and finance ministers on Wednesday, delegations from several countries, including U.S. Treasury Secretary Janet Yellen, walked out of the room while Russia's delegate began his remarks, the White House confirmed.

Canada's Finance Minister, Chrystia Freeland, tweeted a photo of several officials, including herself, Yellen, U.S. Federal Reserve chair Jerome Powell and European Central Bank president Christine Lagarde, outside of the meeting room, standing in solidarity with Ukrainian Finance Minister Serhiy Marchenko.

"It's an indication of the fact that President Putin and Russia has become a pariah on the global stage," White House press secretary Jen Psaki told reporters.

The Treasury also unveiled new sanctions Wednesday against dozens of Russian and Belarusian people and institutions, including a key commercial bank and a virtual currency mining company.

"This is part of our stepped-up effort to crack down on those attempting to evade our unprecedented sanctions," Psaki said.

The State Department has also imposed visa restrictions on over 600 Russians, Belarusians and Ukrainian separatists backed by the Kremlin, Secretary of State Antony Blinken said.

-ABC News' Sarah Kolinovsky and Conor Finnegan

United Nations Secretary-General António Guterres wrote separate letters to Russian President Vladimir Putin and Ukrainian President Volodymyr Zelenskyy on Tuesday asking to meet "to discuss urgent steps to bring about peace in Ukraine," a UN spokesperson said on Wednesday.

Mykhailo Podoliak, adviser to the head of the president's office, tweeted that Ukraine is ready to hold a special round of negotiations in Mariupol.

Four more Russian battalions, each made up of roughly 800 to 1,000 troops, have crossed into Ukraine over the last 24 hours, a senior U.S. defense official said Wednesday. Three of those battalions -- or up to 3,000 troops -- moved to the disputed Donbas region in eastern Ukraine, the official said.

Four flights carrying military aid, including artillery, from the Biden administration's most recent $800 million package arrived in Ukraine over the last 24 hours, the official said. More supplies are set to arrive over the next day, the official said.

When ABC News asked why the U.S. decided to send artillery, the official responded: "We're mindful of the importance of artillery in the fight that they're in right now and in the fighting in the days to come because of the terrain, and because of what we think they're going to be up against with Russian forces."

Another reason was "the fact that it wouldn't require an onerous amount of training for the Ukrainians to know how to use them" and the ability to ship them quickly, according to the official.

-ABC News' Matt Seyler