Biden administration officials on Friday sounded the alarm that a Russian military invasion of Ukraine was an immediate threat, warning that it could happen before the Winter Olympics end on Feb. 20.

Secretary of State Antony Blinken cautioned that “we’re in a window where an invasion could begin anytime,” while President Biden’s national security adviser, Jake Sullivan, told reporters an invasion could begin “any day now.”

The rhetoric marked a rapid escalation of the White House’s warnings of military action by Moscow, which has assembled forces outside the Ukrainian borders over the past few months and been a source of concern for the U.S. and its allies.

Here’s the latest on the possibility of a Russian invasion of Ukraine.

Americans urged to leave immediately

President Biden this week urged Americans to leave Ukraine immediately, warning that the risk of violence breaking out had grown too great to risk staying, something echoed on Friday by Sullivan.

“The risk is now high enough and the threat is now immediate enough that this is what prudence demands,” Sullivan said. “If you stay, you are assuming risk with no guarantee that there will be any other opportunity to leave and no prospect of a U.S. military evacuation in the event of a Russian invasion.”

Sullivan emphasized that Biden would not send U.S. troops into Ukraine for rescue missions should Americans decide to stay and fighting breaks out. He also cautioned that the window to safely evacuate was dwindling, urging American citizens to leave within 24 to 48 hours.

A Russian invasion could begin with aerial attacks that indiscriminately harm civilians, Sullivan said, and could sever lines of communication, shutter roadways and curb commercial flights or trains out of the country.

“I’m not standing here and saying what is going to happen or not happen, I’m only standing here to say … that prudence demands that this is the time to leave now while commercial options and commercial rail and air service exits, while the road remains open,” he said.

Invasion possible before end of Olympics 

Russian President Vladimir Putin’s public show of unity with Chinese President Xi Jinping at the opening ceremony of the Winter Olympics in Beijing on Feb. 2 raised the possibility that the Russian leader would not seek to upstage his “best friend” and launch an invasion amid the two-week sporting competition. 

But U.S. officials have said those assessments are unfounded, with Blinken and Sullivan specifically raising alarm that the Olympics hold no bearing on Putin’s decisionmaking. 

“Russian military action could begin any day now … and it could occur before the Olympics have ended,” Sullivan said.

Blinken, who is meeting with Australian, Japanese and Indian officials for a security dialogue in Australia, echoed that statement. 

“We’re in a window when an invasion could begin at any time. And to be clear, that includes during the Olympics,” he said on Friday in Melbourne. 

U.S. officials have pointed to Putin’s past behavior of launching military action during the 2008 Summer Olympics that also took place in Beijing, when he sent troops to Georgia. The Russian invasion of Crimea also took place days after the 2014 Winter Olympics had ended.

“This marks the second time that Russia has escalated aggression toward a sovereign country during a Beijing Olympics,” Daniel J. Kritenbrink, assistant secretary of State in the Bureau of East Asian and Pacific Affairs said in a briefing with reporters on Feb. 4. 

US unclear on whether Putin has decided to invade

Sullivan emphasized that while the U.S. is prepared for a Russian invasion to happen at any time, the U.S. has not assessed that Putin has ultimately made the decision of whether or not to invade.

“We are not saying that a final decision has been taken by President Putin. What we are saying is that we have a sufficient level of concern, based on what we’re seeing on the ground and what our intelligence analysts have picked up,” Sullivan said. “We are in an urgent situation.”

Despite U.S. warnings, some experts remain skeptical of a full-scale Russian invasion, given the high costs for Russia economically and militarily. 

“I think the war could be painful in many ways for Russia,” said Michael O’Hanlon, senior fellow at the Brookings Institution. 

O’Hanlon predicted that the Russian buildup is part of a coercive effort by Putin to extract concessions on Ukraine security from the U.S. and NATO. 

Still, the U.S. is increasing its military presence in Europe to bolster the defenses of NATO countries. Secretary of Defense Lloyd Austin on Friday said the U.S. is sending an additional 3,000 troops to Poland. This brings the total number of U.S. troops in Europe to 6,000.

Attack on Kyiv a distinct possibility

While Sullivan said U.S. intelligence could not predict with certainty what Russia would do, he warned that Russia targeting the Ukrainian capital city of Kyiv was a possible scenario.

“We’ve been clear that it could take a range of different forms, but I want to be equally clear that one of those forms is a rapid assault on the city of Kyiv,” Sullivan told reporters. 

“That is a possible line of attack, course of action, that the Russian forces could choose to take. They could also choose to move in other parts of Ukraine as well,” he said.

An attack on Kyiv could be devastating for Ukraine. It is the seat of the Ukrainian government, and it is the most populous city in the country at nearly 3 million people. 

“It could be more limited, it could be more expansive, but there are very real possibilities that it will involve the seizure of a significant amount of territory in Ukraine and the seizure of major cities, including the capital city,” Sullivan said when asked about the potential course of a Russian invasion.

Biden continues coordination with allies

Biden and other top administration officials have participated in a flurry of diplomatic engagements regarding Russia and Ukraine over the past several weeks, and those conversations are expected to continue into the weekend.

Biden held a secure video call with the leaders of Canada, Germany, France, the United Kingdom, Poland, Italy and Romania on Friday. 

“The leaders agreed on the importance of coordinated efforts to deter further Russian aggression against Ukraine, including their readiness to impose massive consequences and severe economic costs on Russia should it choose military escalation, and to continue reinforcing the defensive posture on NATO’s eastern flank,” the White House said in a readout of the call. 

Sullivan said that Biden is likely to speak with Putin, but White House officials did not specify when such a conversation would happen. Biden is spending the weekend at Camp David.

White House press secretary Jen Psaki said that the presidential retreat is “fully equipped” for Biden to engage with his national security team as well as European counterparts, but did not offer any specific details on what meetings or phone calls he is expected to have. 

“We are making these decisions about who he will engage with on a day-by-day basis,” Psaki said.

Updated Feb. 12, 8:06 a.m.