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

Russian President Vladimir Putin has ordered his military to put Russia's strategic deterrence forces in a state of heightened readiness, saying it is a response to what he called "aggressive statements" from NATO countries.

In a televised meeting, Putin ordered his defense minister and chief of general staff to move Russia's forces, including the nuclear triad, into a "special regime of combat duty,"

The announcement appears to be intended as rattling Russia's nuclear saber at Western countries as they send large numbers of weapons to Ukraine and sanction Russia.

"Senior officials of the leading NATO countries allow aggressive statements against our country, therefore I order the minister of Defense and the chief of the General Staff to transfer the deterrence forces of the Russian army to a special combat duty regime," Putin said during a meeting with Defense Minister Sergei Shoigu and Chief of the General Staff of the Russian Armed Forces Valery Gerasimov.

-ABC News' Patrick Reevell and Tanya Stukalova

The United States will provide $54 million in humanitarian aid to help Ukrainians, Secretary of State Antony Blinken said on Sunday. 

“This assistance enables humanitarian organizations to support citizens of Ukraine already in need and those newly affected by Russia's unprovoked and unjustified attack,” he said on Twitter. 

With the new funding, the U.S. has provided about $405 million in humanitarian aid to Ukraine since 2014, Ned Price, spokesperson for the State Department, said on Twitter.

Ukrainian President Volodymyr Zelenskyy said on Sunday his government had submitted an application to the International Court of Justice, seeking to hold Russia accountable for its invasion. 

“Russia must be held accountable for manipulating the notion of genocide to justify aggression,” Zelenskyy said on Twitter. “We request an urgent decision ordering Russia to cease military activity now and expect trials to start next week.”

About 368,000 people have fled Ukraine into neighboring countries, as the number of refugees "continues to rise," the U.N. Refugee Agency said on Sunday.

The agency said earlier on Sunday that about 200,000 people crossed Ukraine’s borders as refugees. On Saturday, the figure had been about 150,000 people, said Filippo Grandi, U.N. high commissioner for refugees.