The United States on Monday told families of its government employees in Belarus to leave the country amid fears of a possible Russian invasion of neighboring Ukraine.

The US State Department "ordered the departure of family members of US government employees" from Belarus, according to a travel advisory issued Monday.

It also warned US citizens not to travel to Belarus, citing "the arbitrary enforcement of laws, the risk of detention, and unusual and concerning Russian military buildup along Belarus' border with Ukraine."

The order came hours after Washington and Moscow clashed at the United Nations Security Council over Ukraine.

The US accused Russia of planning to increase its troop presence in Belarus to 30,000 in the coming weeks, to add to the 100,000 it has moved near the Ukrainian-Russian border.

Russian troops in Belarus

According to the US, about 5,000 Russian troops are already in Belarus.

"We've seen evidence that Russia intends to expand that presence to more than 30,000 troops near the Belarus border" with Ukraine by early February, US Ambassador to the UN Linda Thomas-Greenfield said during the Security Council session.

She also said the forces would be "less than two hours north of [the Ukrainian capital] Kyiv."

Washington called Russia's troop deployment on the border a "threat to international peace and security" and threatened to impose sanctions on wealthy Russian oligarchs if Ukraine were attacked.

Moscow's UN envoy Vassily Nebenza hit back, saying the US was engaging "in hysterics" and called the UN summit a "PR stunt."

He added that the troops in Belarus were there for joint military exercises. 

Meanwhile, Belarus denied that it was being used as a staging ground for a Russian invasion of Ukraine.

Tensions between Russia and the West over Ukraine have been rising despite ongoing high-level talks.

Russia responds to US letter

On Monday evening, Russia sent a written response to Washington's proposals to deescalate tensions with Ukraine.

The US state department did not reveal the contents of the letter.

"It would be unproductive to negotiate in public, so we'll leave it up to Russia if they want to discuss their response," a State Department spokesperson said.

She added that Washington would continue to consult its allies and partners, including Ukraine.

Last week, the US government had sent a letter to the Kremlin responding to its concerns about security in Europe.

Moscow has said it has no plans to invade Ukraine but has demanded assurance from NATO to never allow Kyiv membership in the alliance.

Its other demands include rolling back NATO forces in Eastern Europe and ending the deployment of weapons near Russia's borders.

Both the White House and NATO have rejected the core demands as unreasonable, although Russian Foreign Minister Sergey Lavrov said they had made some interesting proposals on what he called "secondary" issues.

adi/msh (AFP, Reuters, dpa)