Russian President Vladimir Putin on Sunday ordered that the country's nuclear deterrence forces be put on alert, ratcheting up tensions over the invasion of Ukraine.

"I order the defense minister and the chief of the general staff of the Russian armed forces to put the deterrence forces of the Russian army into a special mode of combat service," Putin said in a televised address.

The decision comes after Western leaders agreed to a fresh wave of sanctions on Moscow, including freezing Putin's personal assets and cutting some Russian banks from the SWIFT international payments system.

Putin also blamed what he called "aggressive statements" by leading NATO powers.

Doubts raised about nuclear order

The actual effect of the order, however, was not immediately clear. Former Russian military officer Konstantin Eggert told DW he had "trouble discerning" what Putin meant when he said nuclear forces are on higher alert.

"The expression he used to indicate some heightened state of alert does not exist in Russian military manuals," Eggert, DW's Russia affairs analyst said.

There are four levels of alert in the Russian military, he explained. Those four levels are: regular, heightened, the threat of war and full or complete.

"Nuclear forces are pretty much always on heightened alert," Eggert noted.

Putin's latest threat 'unacceptable'

US Ambassador to the United Nations Linda Thomas-Greenfield told CBS: "President Putin is continuing to escalate this war in a manner that is totally unacceptable and we have to continue to stem his actions in the strongest possible way."

NATO Secretary-General Jens Stoltenberg called the order "irresponsible," telling CNN Sunday, "this is dangerous rhetoric."

White House press secretary Jen Psaki told ABC's This Week that Putin was resorting to a pattern he used in the lead-up to the invasion.

Psaki said his strategy was to "manufacture threats that don't exist in order to justify further aggression.''

Retired US general says rhetoric cost 'nothing'

Ben Hodges, a retired US Army general who served as the commanding officer of US Army forces in Europe, told DW that Putin's rhetoric was unsurprising:

"Of course, it cost him nothing, nothing to threaten the use of nuclear weapons," Hodges said.

"If they should make the terrible calculation to employ a nuclear weapon, no matter how large or small, it will cost [Putin] and Russia everything," he added.

Ahead of Thursday's invasion, Putin threatened to retaliate harshly against any direct intervention in the conflict, reminding the world of his country's status as one of the two dominant nuclear powers.

Ukraine to receive new weapons

At least 198 Ukrainians, including three children, have been killed in the invasion, the head of Ukraine's Health Ministry said. Meanwhile, the Ukrainian president's office said negotiations between Kyiv and Moscow would be held at the Belarusian-Ukrainian border. They would meet without preconditions, it said.

At the same time, the EU, the US and its allies authorized more weapons transfers to help Ukraine fight Russia's advance.

On Saturday, Germany reversed a longtime policy of not sending weapons to active conflict zones.

Berlin announced it would deliver 1,000 anti-tank weapons and 500 "Stinger" class surface-to-air missiles to Ukraine.

Germany also said it would allow third countries, the Netherlands and Estonia, to deliver its weapons to Kyiv.

mm/dj (AP, Reuters)