A Russian invasion of Ukraine could begin "any day," including before the end of the Winter Olympics, Biden administration officials warned Friday, sounding a greater sense of urgency about the threat of military movement by Moscow.

"It could begin any day now, and it could occur before the Olympics have ended," White House national security adviser Jake Sullivan told reporters during a White House briefing. The Beijing Olympics are scheduled to conclude on Feb. 20.

"I’m not going to get into intelligence information, but if you look at the disposition of intelligence forces ... the Russians are in a position to be able to mount a major military action in Ukraine any day, and for that reason we believe that it is important for us to communicate to our allies and partners, to the Ukrainians and to the American citizens who are still there," Sullivan said.

"I want to be clear though: We are not saying a final decision has been taken by President Putin," he continued. "What we are saying is we have a sufficient level of concern based on what we have seen on the ground and what our intelligence analysts have picked up that we are sending this clear message."

"PBS Newshour" reported shortly before Sullivan briefed reporters that Western officials believe Putin has made up his mind, decided to invade Ukraine and communicated that decision to Russian military leaders.

Sullivan denied that that report was accurate when it was described to him during the briefing on Friday, saying that the U.S. government still does not believe that Putin has made his call.

Sullivan added that President Biden is likely to speak by phone with Putin but had no timing to announce as of Friday afternoon.

He also emphasized that Americans in Ukraine should seek to leave.

Sullivan's comments echoed those of Secretary of State Antony Blinken, who said earlier Friday "we're in a window" with the potential for an invasion.

Biden administration officials have been sounding the alarm for weeks that a Russian invasion of Ukraine was possible as Moscow amassed troops and military equipment at the border of the two countries. They have pledged to levy severe economic sanctions against Russia should it act, and officials have projected unity with NATO allies.

Biden said earlier this week that he did not believe Putin had decided whether to launch an incursion into Ukraine. Biden held a phone call earlier Friday with U.S. allies to discuss strategy on deterring Russian action against Ukraine.

He and several other administration officials have urged Americans who are in Ukraine to leave the country, citing the risk of violence breaking out should Russia make a move.

Sullivan stressed Friday that Biden had no intention of sending U.S. troops on a rescue mission into Ukraine for Americans who are still in the country.

"The risk is now high enough and the threat is now immediate enough that this is what prudence demands," he 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 suggested a Russian attack would likely begin with aerial bombings and missile strikes that could kill civilians indiscriminately. He did not speculate on what the goal of an invasion would be, but acknowledged “there are very real possibilities that it will involve the seizure of a significant amount of territory in Ukraine,” including a major city like the capital Kyiv.

Updated at 2:36 p.m.