US President Barack Obama and Vice President Joe Biden expressed concerns about fresh tensions between Russia and Georgia in telephone calls with the leaders of the rival ex-Soviet states.
The White House said Russian President Dmitry Medvedev called Obama to wish him a happy 48th birthday, and that the leaders discussed the need to ease rattled nerves in the region, a year on from a Russia-Georgia war.
Biden called Georgian President Mikheil Saakashvili and expressed concern over the situation, as Georgia warned of the risk of a new war with Russia and Moscow raised the battle-readiness of its forces, ahead of the anniversary of their conflict over rebel South Ossetia.
"Russian President Medvedev called President Obama today to wish him happy birthday," the White House said in a press statement.
"During the call, the presidents discussed the situation in Georgia and the need to decrease tensions in the region.
"President Obama reiterated the importance of working through established crisis management mechanisms such as the Joint Incident Prevention and Response Mechanism and underscored the need for international monitors."
|Russian soldiers guard a checkpoint near the Georgian village of Khurvaleti in 2008|
Later, the White House said Biden called Saakashvili to "discuss the current situation in Georgia."
"He also underscored the importance of having an objective international monitoring mission with access to both sides of the boundary line.
"Vice President Biden reiterated US support for Georgia's democracy."
Saakashvili had earlier called on the United States and the European Union to send a "clear message" to Moscow to help avert a new war, as both sides exchanged accusations of attacks and "provocations" in the region.
The Russian foreign ministry meanwhile said its forces had heightened their state of battle-readiness in South Ossetia.
"The situation is very worrying and the Georgian provocations ahead of the anniversary of last year's war are not halting," foreign ministry spokesman Andrei Nesterenko said in a statement.
Obama's administration is walking a tightrope between its desire to reset ties with Moscow and showing support for its ally Georgia, as tensions rise again between Moscow and Tbilisi.
Russia smashed a Georgian military offensive to recapture South Ossetia in a brief war in August last year, sending relations between Moscow and Washington during the final months of George W. Bush's administration to post-Cold War lows.
Biden risked irking Russia last month when he said in a speech in the ex-Soviet republic that Obama backed Georgia's aspiration to join NATO.
He also reiterated long-standing US policy on Georgia's territorial integrity, saying Washington sought a "free, secure, democratic, united Georgia."
Moscow has recognized two rebel regions of Georgia -- Abkhazia and South Ossetia -- as independent states, prompting condemnation from around the world.
The war erupted last year when an attempt by Georgian troops to retake South Ossetia was rebuffed by Russia. Moscow then sent troops and tanks deep into Georgian territory.
After the war, Russian forces mostly withdrew into South Ossetia and Abkhazia but Moscow then infuriated the West with the independence move.
The White House also said that Obama and Medvedev used Tuesday's conversation to discuss the need to "move forward quickly" on agreements reached at their summit last month in Moscow.
"In particular, the presidents reaffirmed their commitment to complete negotiations on a follow-on agreement to START by December of this year."
Obama and Medvedev signed a declaration in Moscow pledging to reach a new nuclear arms pact to replace the 1991 Strategic Arms Reduction Treaty.