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.

Hours before the physical invasion into Ukraine, Microsoft detected a new round of "offensive and destructive" cyberattacks directed at the Ukrainian government, a top Microsoft official announced.

"In recent days, we have provided threat intelligence and defensive suggestions to Ukrainian officials regarding attacks on a range of targets, including Ukrainian military institutions and manufacturers and several other Ukrainian government agencies," President and Vice Chair of Microsoft Brad Smith wrote in a blog post Monday. "This work is ongoing."

Microsoft remains concerned about the cyber threat emanating from Ukraine, "especially" recent cyberattacks on Ukrainian civilian digital targets, including on the financial sector, agriculture sector, emergency response services, humanitarian aid efforts and energy sector organizations, Smith said.

"These attacks on civilian targets raise serious concerns under the Geneva Convention, and we have shared information with the Ukrainian government about each of them," he wrote.

Microsoft has advised the Ukrainian government about recent cyber efforts to steal a wide range of data, including health, insurance and transportation-related personally identifiable information, as well as other government data sets, Smith said. Microsoft is also sharing information with U.S. officials.

Over the weekend, the U.S. warned that a cyberattack in Ukraine could have ripple effects in the U.S.

"Further disruptive cyberattacks against organizations in Ukraine are likely to occur and may unintentionally spill over to organizations in other countries," the FBI, DHS and CISA warned in a statement, saying Russia has taken these steps in the past. "Organizations should increase vigilance and evaluate their capabilities encompassing planning, preparation, detection, and response for such an event."

Microsoft is "swiftly" removing Russian propaganda from their websites from the Windows app store, including RT, the Russian state-controlled international television network.

"We are also focused as a company in protecting against state-sponsored disinformation campaigns, which have long been commonplace in times of war," Smith wrote.

This comes as Meta, the parent company of Facebook, announced efforts it was taking to disrupt social media misinformation campaigns.

-ABC News’ Luke Barr and Cindy Smith