WATCH: Pentagon press secretary John Kirby holds briefing on Russia’s activities in Ukraine

The White House says U.S. intelligence officials have determined a Russian effort is underway to create a pretext for its troops to further invade Ukraine, and Moscow has already prepositioned operatives to conduct “a false-flag operation” in eastern Ukraine.

Watch the briefing in the video player above.

White House press secretary Jen Psaki said the intelligence findings show Russia is also laying the groundwork through a social media disinformation campaign that frames Ukraine as an aggressor in the crisis.

Psaki charged that Russia has already dispatched operatives trained in urban warfare who could use explosives to carry out acts of sabotage against Russia’s own proxy forces – blaming the acts on Ukraine – if Russian President Vladimir Putin decides he wants to move forward with an invasion.

Pentagon spokesman John Kirby described the intelligence as “very credible.”

“We’ve seen this kind of thing before out of Russia, when there isn’t an actual crisis to suit their needs. They’ll make one up,” he added.

The U.S. intelligence findings, which were declassified and shared with U.S. allies before being made public, estimate that a military invasion could begin between mid-January and mid-February.

Ukraine is also monitoring the potential use of disinformation by Russia. Separately, Ukrainian media on Friday reported that authorities believed Russian special services were planning a possible false flag incident to provoke additional conflict.

The new U.S. intelligence was unveiled after a series of talks between Russia and the U.S. and its Western allies this week in Europe aimed at heading off the escalating crisis made little progress.

In addition, a cyberattack left a number of Ukrainian government websites temporarily unavailable Friday, officials said.

Kirby told reporters “One could imagine, right, that an attack like that is meant to disrupt capability to try to dissuade action, to try to change the behaviors or the leadership decisions inside Ukraine. I mean, any number of reasons, not to mention just to intimidate.”

It wasn’t immediately clear who was responsible the cyber disruption which came amid heightened tensions with Russia.

Ukrainian Foreign Ministry spokesman Oleg Nikolenko told The Associated Press it was too soon to say who was behind it, “but there is a long record of Russian cyber assaults against Ukraine in the past.”

Moscow had previously denied involvement in cyberattacks against Ukraine.