A Russian invasion of Ukraine could be imminent, White House national security adviser Jake Sullivan warned on Sunday, Eurasia Diary reports citing CNBC news. 

“We are in the window,” Sullivan said in an interview on “Fox News Sunday.” “Any day now, Russia could take military action against Ukraine or it could be a couple of weeks from now, or Russia could choose to take the diplomatic path instead.”

Sullivan appeared on several morning news programs to discuss the ongoing situation in Eastern Europe.

His appearances come after two U.S. officials said Russia has in place about 70% of the combat power it believes it would need for a full-scale invasion of Ukraine. The number of battalion tactical groups in the border region has risen to 83 from 60 as of Friday and 14 more are in transit, according to Reuters.

“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 said on NBC’s “Meet the Press.”

The form of attack could take different forms, Sullivan told NBC. Possible attacks could include annexing Ukraine’s Donbass region, cyberattacks or a full-scale invasion.

“Part of the reason we’ve been working so intensively over the last few months is not just to prepare for one contingency but to prepare for all contingencies and to work with our allies and partners on what a response would look like in each of those instances,” Sullivan said.

The U.S. and its allies have been clear the nations would act aggressively if Russia launches an attack. The U.S., for example, has threatened severe sanctions if Russian President Vladimir Putin invades.

The timeline for diplomatic negotiations could be dwindling.

“We believe that there is a very distinct possibility that Vladimir Putin will order an attack on Ukraine,” Sullivan said on ABC’s “This Week.”

If a full-scale Russian invasion occurs, thousands of civilians and troops could die, according to Reuters.

Ukraine could suffer 5,000 to 25,000 troop casualties, the outlet reported, citing a U.S. official. Russia’s troop casualties could be between 3,000 and 10,000, and civilian casualties could range from 25,000 to 50,000, according to U.S. estimates. It would also prompt millions of Ukrainians to be displaced.

Sullivan on Sunday did not comment on the projections but warned of the impact on Ukraine.

“If they choose to go down the path of escalation instead, it will come at enormous human cost to Ukrainians. But it will also, we believe, over time, come at real strategic cost to Vladimir Putin,” Sullivan told ABC.