The United States now believes a Russian invasion of Ukraine “could happen at any time,” White House National Security Advisor Jake Sullivan said Sunday, in what would be the biggest military operation in Europe since World War II.

“We believe that the Russians have put in place the capabilities to mount a significant military operation into Ukraine, and we have been working hard to prepare a response,” Sullivan told NBC’s “Meet the Press” show.

In a separate interview on “Fox News Sunday,” Sullivan said, “Any day Russia could take action against Ukraine, or it could be a couple weeks,” with U.S. intelligence officials assessing that Moscow has 70% of its strike force in place for an attack.

He said a Russian invasion would come “at an enormous human cost to Ukraine but at a strategic cost to Russia,” with the U.S. prepared to impose swift and severe economic sanctions against Russia to hobble its economy.

“Whatever actions Russia takes next, America is ready,” Sullivan said.

Sullivan, however, said the U.S. is willing to negotiate with Russian President Vladimir Putin over his professed security concerns about actions of the U.S. and its 29 NATO allies.

“That includes the placement of certain range systems of missiles,” Sullivan said. “It includes transparency around military exercises. It includes greater capacity to have a confidence building and to avoid incidents that could lead to escalation or miscalculation.”

“But what we're not prepared to negotiate are the fundamental principles of security that include an open door to NATO for countries who can meet the requirements,” Sullivan said in rejecting Putin’s demand that NATO rule out the possibility of Ukrainian membership.

The Western allies say no outside nation has veto power over which countries join the Atlantic alliance.

U.S. President Joe Biden last week ordered that 3,000 American troops be sent to two eastern NATO countries, Poland and Romania. Reports say troops from the U.S. 82nd Airborne Division have landed in southeastern Poland near the border with Ukraine.

Washington has ruled out dispatching troops to fight alongside Ukrainian forces in the event of a Russian invasion. The U.S. has, however, sent $500 million worth of arms and defensive missiles to the Kyiv government.

If Russia invades Ukraine, then cuts off its natural gas supplies to European countries in retaliation to U.S. sanctions, Sullivan said the U.S. is moving to help redirect natural gas supplies from elsewhere to its European allies.

In any event, Sullivan said if Russia invades Ukraine, its Nord Stream 2 natural gas pipeline running under the Baltic Sea from Russia to Germany “will not move forward.” The pipeline is completed but not yet operational.

In the NBC interview, Sullivan said Biden “has rallied our allies. He's reinforced and reassured our partners on the eastern flank. He's provided material support to the Ukrainians, and he's offered the Russians a diplomatic path if that's what they choose instead, but either way, we are ready, our allies are ready and we're trying to help the Ukrainian people get ready as well.” (VOA)

•PHOTO: This handout satellite image released by Maxar Technologies shows a close up of armored personnel carriers and trucks at Russia’s Klimovo storage facility, in Bryansk Oblast, 13 kilometers north of the Russia/Ukraine border, Jan. 19, 2022

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