Russia has asked two US military officials attached to the US embassy in Moscow to leave the country, a US official confirmed Thursday, dpa reported.
"We object to this action but we'll comply with the Russian government's request," Edgar Vasquez, a spokesman at the US State Department, told Deutsche Presse-Agentur dpa.
US officials said they did not know the reason for the expulsion.
They could not confirm reports that over the past six months, the US has asked two Russian diplomats to leave the United states.
In Moscow, the Russian Foreign Ministry refused comment on the expulsions of the US military attaches.
The news emerged at a vulnerable moment in US-Russian relations, as new Russian President Dmitry Medvedev spent his first day in office.
On Wednesday, Stephen Hadley, national security advisor to US President George W Bush, called for Russia to "back down" from intervening in neighbouring Georgia's affairs.
On Thursday, Russia's military announced it would increase its troops in Georgia's breakaway region of Abkhazia to counter Georgia's accumulating military forces in the contested region. Russia's peacekeepers in Abkhazia will increase to 2,542 troops, under the maximum permitted of 3,000 as provided for by the UN ceasefire.
Georgian President Mikhail Saakashvili said the move put Georgia "very close" to war with Russia and the "threat remained" for a breakout over its breakaway region of Abkhazia.
Abkhazia and South Ossetia, two regions with Russian populations, have been autonomous since civil wars ended in the early 1990s, and South Ossetia has also been targetted by Russia in a similar fashion.
Tension has also risen between the US and Russia over US plans to base missile defence in Europe. Washington has also been a critic of Putin's alleged crackdowns on democratic institutions and civic organizations.