Russia-Ukraine updates: US to ban Russian carriers from its airspace

The International Criminal Court is "opening an investigation into the situation in Ukraine, as rapidly as possible," the court's chief prosecutor, Karim A.A. Khan, announced Monday.

The court has "reasonable basis to believe" that war crimes and crimes against humanity were committed in Ukraine and is pursuing accountability, including possible prosecutions, Khan said in a statement.

An authorization from a pretrial chamber of the court and support and funding from the ICC's 123 member states will be required to begin an investigation.

Neither Russia nor Ukraine is a member of the court, but Ukraine has provided authorization for an investigation in its territory, Khan said.

The U.N. Human Rights Council also voted Monday to hold an urgent debate on Thursday, where they'll consider a draft resolution from Ukraine.

-ABC News' Conor Finnegan

Americans people should not be worried about the threat of nuclear war, President Joe Biden said Monday.

The president made the comment while leaving a White House event celebrating Black History Month, replying “No” when a reporter asked whether the country should feel worried.

The brief response to the question was Biden's only reference to the current situation in Ukraine, but Vice President Kamala Harris commented further on the situation unfolding in Eastern Europe.

"Today the eyes of the world are on Ukraine, and the brave people who are fighting to protect their country and their democracy," Harris said. "And their bravery is a reminder, a most recent reminder that justice, equality, and freedom must never be taken for granted by any of us."

On a call with allies Monday afternoon, Biden discussed "their coordinated efforts to impose severe costs and consequences to hold Russia accountable while working to maintain global economic stability, including with regard to energy prices,” according to a statement from the White House.

The U.S. sees "no reason" to change its own nuclear alert level, White House press secretary Jen Psaki said in a press briefing Monday afternoon.

“We are assessing Putin's directive and at this time we see no reason to change our own alert level,” she said.

-ABC News' Mary Bruce and Molly Nagle

Twelve Russian diplomats have been expelled from Moscow’s mission to the United Nations in New York, U.S. Ambassador Richard Mills, the deputy representative to the U.N., confirmed on Monday.

Those diplomats were engaged in activities not in accordance with their obligations and responsibilities as diplomats, Mills said.

They "abused their privileges of residency in the U.S. by engaging in espionage activities that are adverse to our national security," Olivia Dalton, spokeswoman for U.S. Ambassador Linda Thomas-Greenfield, tweeted Monday. The action to expel them “has been in the works for several months,” Dalton wrote.

Russian Permanent Representative to the U.N. Vasily Nebenzya in a Monday press conference in New York accused U.S. authorities of undertaking "another hostile action against the Russian Federation's mission to the United Nations" and of "grossly violating their commitments on the host country agreement that they undertook" with this move.

The expelled employees are now considered "personae non gratae" and were ordered to leave the U.S. by March 7, according to Nebenzya.

-ABC News’ Conor Finnegan and Tanya Stukalova

The U.S. is supporting an international effort to "detect and document potential human rights violations" for abuses of international humanitarian law, potential war crimes and "other potential atrocities" committed by Russia, Department of State Spokesman Ned Price announced Monday.

The U.S. will use "every tool available, including criminal prosecutions where appropriate," Price said in a warning to "the government of Russia and all Russian personnel involved in these operations" against Ukraine.

Price said the U.S. is concerned by reports of civilians killed, schools and kindergartens destroyed, and other civilian targets impacted.