The US believes Russia is planning to invade Ukraine “as soon as early 2022” with an estimated 175,000 troops — in a sign of the escalating alarm in Washington about Moscow’s intentions towards its neighbour.

A Biden administration official said on Friday night that Moscow’s plans “call for a military offensive against Ukraine as soon as early 2022 with a scale of forces twice what we saw this past spring during Russia’s rapid military build-up near Ukraine’s borders”.

This included “extensive movement of 100 battalion tactical groups with an estimated 175,000 personnel, along with armour, artillery and equipment”.

According to the administration official, half the units were already near Ukraine’s border, having arrived in the past month. Russia had already moved to established a “ready reserve of contract reservists” to prepare for the offensive.

Before heading to the presidential retreat at Camp David on Friday evening, Joe Biden said: “We’ve been aware of Russia’s actions for a long time and my expectation is we’re going to have a long discussion.”

Details of the US assessment of Russia’s plans, first reported by The Washington Post, emerged a few hours after Biden said he was in “constant contact” with European allies and Ukraine about Moscow’s threat. He warned that he would try to stop Russian president Vladimir Putin from following through with this plans, hinting at punitive measures.

“What I am doing is putting together what I believe . . . will be the most comprehensive and meaningful set of initiatives to make it very, very difficult for Mr Putin to go ahead and do what people are worried he may do,” the US president said. “But that’s in play right now,” Biden added.

A spokesperson for the White House’s National Security Council said Washington was “deeply concerned by evidence that Russia is stepping up its planning for significant military action against Ukraine” — noting this had been discussed by Antony Blinken, US secretary of state, on a trip to Europe this week.

“The Biden administration has been consistent in our message to Russia: the United States does not seek conflict, and the best way to avert a crisis and a negative spiral in the broader relationship is through diplomacy and de-escalation,” the NSC spokesperson said.

The Russian embassy in Washington did not immediately respond to a request for comment.

The strength of the US intelligence assessment has surprised some European officials, and authorities on both sides of the Atlantic have spent weeks comparing and contrasting their evaluations. The Biden administration is seeking to flag the risks of a Ukraine invasion as part of a diplomatic push to deter Putin from deciding to act.

A US defence official last week told the Financial Times that the Biden administration was considering providing weaponry to Ukraine, but that inter-agency discussions were continuing and no decisions had yet been made.

The official said the US was “mindful of what we are seeing” close to the Ukrainian border, and that if weapons were provided, that would help the Ukrainians defend themselves if attacked.

Earlier on Friday an administration official said: “Since the beginning of this administration we have demonstrated that the United States and our allies are willing to use a number of tools to address harmful Russian actions, and we will not hesitate from making use of those and other tools in the future.”