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

A senior U.S. defense official said Tuesday that the United States cannot confirm whether Russia used chemical agents in Mariupol or elsewhere in Ukraine but that the Pentagon is concerned Russian forces could disguise such attacks.

The Department of Defense has seen evidence Russia has considered disguising the use of chemical weapons by making them appear to be more benign riot control agents, the official said.

"In the past we've had indications that that could be one thing that the Russians look at is the potential mixing of agents with the idea that they could disguise a more serious attack by using the vehicle and the techniques of riot control agents," the official said.

Pentagon press secretary John Kirby released a similar statement Monday night to address social media reports claiming Russia used a chemical weapon in Mariupol.

"These reports, if true, are deeply concerning and reflective of concerns that we have had about Russia’s potential to use a variety of riot control agents, including tear gas mixed with chemical agents, in Ukraine," Kirby said.

-ABC News' Matt Seyler

U.S. Secretary of State Antony Blinken was meeting Tuesday morning with U.N. refugee agency chief Filippo Grandi amid the crisis in Ukraine and other upheavals that have displaced people around the globe.

"We've only seen that challenge increase and, of course, Ukraine is now added to the mix with Russian aggression displacing, within Ukraine or outside of Ukraine, two-thirds of the children in that country, as well as, of course, many, many adults," Blinken said while sitting across the table from Grandi.

There are some 95 million people displaced across the globe, with the number of refugees alone larger than the populations of Spain or South Korea, Blinken said.

Blinken added the United States is "grateful" for the work the U.N. High Commissioner for Refugees is doing to meet the needs of refugees. He said the United States is working with the agency to both resettle refugees in the United States and care for refugee populations overseas.

Grandi praised the United States for being the largest donor and the largest resettlement country for refugees.

But weeks after the Biden administration said it would admit up to 100,000 Ukrainian refugees, Grandi said the White House has released no details about how the United States will do that.

"This figure that he (Blinken) mentioned -- 95 million -- maybe 96 million by today, who knows?" Grandi said, adding that the number of refugees had gone up by 12 million in less than two months with the crisis in Ukraine.

Grandi noted other crises from Afghanistan to Africa and Venezuela that have displaced people and said of Russia's war in Ukraine, "That crisis should not make us forget everything else."

-ABC News Conor Finnegan

Russian President Vladimir Putin said Tuesday that his country's "special military operation" in Ukraine would undoubtedly achieve its "noble" objectives."

"On the one hand, we are helping and saving people, and on the other, we are simply taking measures to ensure the security of Russia itself," Putin said, according to Russian news agencies. "It's clear that we didn't have a choice. It was the right decision."

Putin made the comments while visiting the Vostochny Cosmodrome, a Russian spaceport in the Amur Oblast in the Russian Far East, to mark Russia's annual Cosmonautics Day.

He was joined by Belarusian President Alexander Lukashenko. The two leaders held talks on bilateral relations and the situation in Ukraine, without the participation of Russian or Ukrainian delegations.

Nine humanitarian corridors are expected to open in eastern Ukraine again on Tuesday to allow civilians escape heavy fighting, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

She said in a statement via social media Tuesday that evacuation routes were agreed upon for those traveling by private cars from besieged Mariupol in the Donetsk Oblast, as well as from Berdyansk, Tokmak and Enerhodar in the Zaporizhzhia Oblast -- all of which lead to the southeastern city of Zaporizhzhia.

In the Luhansk Oblast, Vereshchuk said routes were established from the cities of Severodonetsk, Lysychansk, Popasna, Hirske and Rubizhne, leading to the city of Bakhmut in the Donetsk Oblast.

The same routes were opened Monday, allowing a total of 4,354 people to evacuate via buses and private cars, according to Vereshchuk. However, Vereshchuk said buses carrying people from Berdyansk, Tokmak and Enerhodar to Zaporizhzhia city were being held up by Russian forces at a checkpoint in Vasylivka for a third day in a row.