U.S. national security adviser Jake Sullivan gives a statement about the situation in Afghanistan during a news briefing at the White House in Washington, U.S., August 23, 2021.
U.S. national security adviser Jake Sullivan gives a statement about the situation in Afghanistan during a news briefing at the White House in Washington, U.S., August 23, 2021. Reuters / LEAH MILLIS

Russia now has enough forces to conduct a major military operation against Ukraine and an assault aimed at seizing large parts of that country could begin "any day now," White House national security adviser Jake Sullivan said on Friday.

Sullivan, speaking at a White House briefing without listing specific evidence, said any American still in Ukraine should leave in the next 24-48 hours. He said a Russian invasion could start with an air assault that would make departures difficult.

Sullivan said U.S. intelligence believes Russian President Vladimir Putin could order an invasion before the end of the Winter Games in Beijing on Feb. 20 and that a rapid assault on the Ukraine capital Kyiv is a possibility.

Sullivan spoke after President Joe Biden held a secure video call with transatlantic leaders from the White House Situation Room and sought allied unity in the face of a worsening situation.

It remains unclear, Sullivan said, whether Putin has definitively given an order to start an invasion. He said he expects Biden to seek out a phone call with Putin soon on the crisis.

"We have not seen anything come to us that says a final decision has been taken, the go-order has been given," he said.

But with 100,000 troops massed on Ukraine's border, Sullivan said a Russian invasion could involve seizure of large sections of Ukraine as well as major cities including Kyiv.

Sullivan said there is a "fundamental distinction" between the intelligence situation now and that which the United States used in justifying the 2003 Iraq war, which was based on claims of weapons of mass destruction that turned out to be wrong.

Then, U.S. "intelligence was used and deployed from this very podium to start a war. We are trying to stop a war, to prevent a war," he said.

Further, he said, in 2003 "it was information about intentions, about hidden things, stuff that couldn't be seen. Today we are talking about more than 100,000 Russian troops amassed along the Ukrainian border... it's all over social media, it's all over your news sites. So, you can believe your own eyes."