Vladimir Putin orders military to put nuclear deterrent forces on high alert, US ambassador accuses Russia of 'continuing to escalate this war'

Vladimir Putin has ordered his military command to put Russia's nuclear deterrence forces on high alert on Sunday as tensions with the West escalate over the invasion of Ukraine.

Putin blamed "aggressive statements" by NATO members and hard-hitting economic sanctions against Moscow as the reason for increasing Russia's preparedness to launch nuclear weapons.

"Western countries aren't only taking unfriendly actions against our country in the economic sphere, but top officials from leading NATO members made aggressive statements regarding our country," Putin said on state television, according to the Associated Press.

"Senior officials of the leading Nato countries also allow aggressive statements against our country, therefore I order the minister of defense and the chief of the general staff [of the Russian armed forces] to transfer the deterrence forces of the Russian army to a special mode of combat duty," Putin added in the appearance with top Russian military officials.

The order came at a meeting between the president, the defense minister, Sergei Shoigu, and the chief of the general staff of the armed forces of Russia, Valery Gerasimov, the Guardian reported.

At the meeting, Putin ordered his top military command to put the nuclear deterrent forces in a "special regime of combat duty."

U.S. Ambassador Linda Thomas-Greenfield condemned the decision as a "totally unacceptable" escalation.

"President Putin is continuing to escalate this war in a manner that is totally unacceptable, and we have to continue to condemn his actions in the strongest possible way," Thomas-Greenfield said during an appearance on "Face the Nation."

Thomas-Greenfield declared that the U.S. will "continue here at the United Nations and around the world to use every possible lever we have at our disposal to expose his actions."

Time magazine reported, "The practical meaning of Putin's order was not immediately clear. Russia and the United States typically have the land- and submarine-based segments of their strategic nuclear forces on alert and prepared for combat at all times, but nuclear-capable bombers and other aircraft are not."

Putin's decision to place Russia's nuclear deterrence forces on high alert comes after several Western countries have pledged military aid to Ukraine.

Also on Sunday, Ukraine agreed to peace talks with Russia on the Ukrainian-Belarusian border.