The White House has increased its threat assessment against Russia ahead of a top US and Russian diplomats meeting.

"We've reached a point where Russia might launch an attack on Ukraine at any time," Press Secretary Jen Psaki told reporters Tuesday.

"I would argue that is more stark than we have ever been."

Psaki's assessment of the situation around Ukraine came ahead of Secretary of State Antony Blinken's Friday meeting in Geneva with Russian Foreign Minister Sergey Lavrov.

According to a US official who requested anonymity, Blinken's objective was to determine "whether there is a diplomatic off-ramp" and "shared ground" on which Russia could be convinced to withdraw from Ukraine.

Ukraine, the United States, and other European countries have expressed grave worry over Russia's army buildup along the border, despite Moscow's repeated assertions that an invasion is planned.

If President Vladimir Putin chose to invade Ukraine, where Russia has already invaded Crimea and backed pro-Russian separatists in another region, Psaki warned of "serious economic consequences."

Nord Stream 2 is listed as a sanctioned project.

While the US and its European allies have no preparations to respond militarily to a Russian war on Ukraine, Washington insists the economic countermeasures would be unprecedented.

Psaki emphasized that this may involve the cancellation of Russia's Nord Stream 2 natural gas pipeline to Germany.

The pipeline, which has been constructed but not yet commissioned, is viewed as a critical component of Europe's energy supply network and the crown jewel of Moscow's export capabilities.

"Our position remains that preventing the Nord Stream 2 pipeline is a credible piece of leverage we have over Russia," Psaki said.

Blinken was scheduled to fly to Ukraine on Tuesday as a gesture of support.

He will then travel to Berlin for four-way discussions with the United Kingdom, France, and Germany to achieve Western unification.

Russian forces have arrived in Belarus.

Meanwhile, a senior US State Department official worried that Russian forces stationed in Belarus for what Moscow and Minsk describe as joint military drills could invade neighboring Ukraine.

Russians will gain improved capacity, opportunity, and channels for launching such an assault due to the war games, a State Department official told reporters during a briefing.

The US is particularly concerned that Belarus's draft constitutional revisions could result in the deployment of Russian nuclear weapons, a senior State Department official told reporters.

Joint military exercises between Russia and Belarus announced by Minsk on Tuesday as Russian troops landed in the nation were "beyond routine" and might serve as a precursor to a permanent Russian military presence including conventional and nuclear weaponry, an official said.