* US says families of American diplomats must leave Ukraine
* President Joe Biden mulling additional troops for region
* UK says Moscow wants to put pro-Russian leader in Ukraine (Adds Ukrainian foreign ministry comment)
By David Shepardson and Paul Sandle
WASHINGTON/LONDON, Jan 24 (Reuters) - The U.S. State Department announced Sunday it was ordering diplomats' family members to leave Ukraine, as U.S. President Joe Biden weighed options for boosting America's military assets in Eastern Europe to counter a buildup of Russian troops.
The order, which also allowed U.S. diplomats stationed at the embassy in the Ukrainian capital Kyiv to leave voluntarily, was one of the clearest signs yet that American officials are bracing for an aggressive Russian move in the region.
"Military action by Russia could come at any time," the U.S. Embassy said https://www.reuters.com/world/us/us-orders-departure-ukraine-embassy-staff-family-members-2022-01-23 in a statement. Officials "will not be in a position to evacuate American citizens in such a contingency, so U.S. citizens currently present in Ukraine should plan accordingly," it added.
Ukrainian foreign ministry said in a statement that it considered the move as "premature and a manifestation of excessive caution."
"In fact, there have been no cardinal changes in the security situation recently: the threat of new waves of Russian aggression has remained constant since 2014 and the buildup of Russian troops near the state border began in April last year," it said.
Tensions in Ukraine have been increasing for months after the Kremlin massed some 100,000 troops near Ukraine's borders, a dramatic buildup the West says is preparation for a war to prevent Ukraine from ever joining the NATO Western security alliance.
The Kremlin has repeatedly denied planning to invade, but the Russian military already tore off a chunk of Ukrainian territory when it seized Crimea and backed separatist forces who took control of large parts of eastern Ukraine eight years ago.
The State Department's announcement comes a day after British authorities said they had information the Russian government was considering a former Ukrainian lawmaker https://www.reuters.com/world/uk/uk-accuses-kremlin-trying-install-pro-russian-leader-ukraine-2022-01-22 as a potential candidate to head a pro-Russian leadership in Kyiv.
The Russian Foreign Ministry dismissed the British allegation as "disinformation," accusing NATO of "escalating tensions" over Ukraine.
TROOPS AND SANCTIONS
Biden has begun considering options for boosting America's military assets in the region, senior administration officials said, after meeting with top national security aides at his Camp David retreat on Saturday.
The New York Times said Biden was mulling plans to send 1,000 to 5,000 troops to Eastern European countries, with the possibility of increasing the number should tensions flare further.
A senior administration official declined to confirm the numbers on Sunday but said "we are developing plans and we are consulting with allies to determine options moving forward."
The United States has sent military assistance to Ukraine but has so far held back from sending American personnel.
U.S. Secretary of State Antony Blinken has rebuffed calls to immediately impose economic sanctions on Russia, saying on Sunday that doing so would undercut the West's ability to deter potential Russian aggression against Ukraine.
Blinken was due to meet virtually with members of the European Union's Foreign Affairs Committee on Monday.
As U.S. troop deployments were discussed, a separate senior administration official said U.S. economic penalties on Russia would have far-reaching consequences should it drive any further into Ukraine.
The United States would use the Foreign Direct Product Rule to restrict the export to Russia of products incorporating microelectronics based on U.S. equipment, software or technology.
Britain has also promised stiff sanctions, with British Deputy Prime Minister Dominic Raab telling Sky News there would be "very serious consequences if Russia takes this move to try and invade."
British officials say they have information the Russian government was considering former Ukrainian lawmaker Yevhen Murayev as a potential candidate to head a pro-Russian government in Kyiv.
Murayev poured cold water on the notion.
"This morning I already read in all the news publications this conspiracy theory: absolutely unproven, absolutely unfounded," Murayev told Reuters https://www.reuters.com/world/uk/ukrainian-politician-mocks-stupid-uk-claims-he-could-lead-kremlin-puppet-2022-01-23 in a video call, adding he was considering legal action.
He denied having any contact with Russian intelligence officers and dismissed the idea that he could be in league with the Kremlin as "stupid," given he was placed under Russian sanctions in 2018.
Although he says he wants Ukraine to be independent from Russia as well as the West, Murayev https://www.reuters.com/world/who-is-yevhen-murayev-named-by-britain-kremlins-pick-lead-ukraine-2022-01-23, 45, has promoted some views that align with the Kremlin's narratives on Ukraine.
The British foreign ministry declined to provide evidence to back its accusations.
In a message to Reuters, Mykhailo Podolyak, a Ukrainian adviser to the presidential office, said there was doubt among Ukrainians as to whether Murayev was "too ridiculous a figure" to be the Kremlin's pick to lead Ukraine.
But Russia had propped up previously minor figures in leadership positions in annexed Crimea and separatist-held eastern Ukraine, he added.
Therefore "one should take this information as seriously as possible," he said.
(Reporting by Michael Holden and Paul Sandle in London, Natalia Zinets in Kyiv; Additional reporting by Matthias Williams in Kyiv, Vladimir Soldatkin in Moscow, and David Shepardson and Steve Holland in Washington; Writing by Raphael Satter, Raissa Kasolowsky, and Frances Kerry; Editing by Alexander Smith, Chris Reese, Kenneth Maxwell and Lincoln Feast.)