The Obama administration said Wednesday is was considering how to respond to a Russian proposal for military talks over Syria, where Moscow is expanding its forces even as US warplanes conduct daily air strikes against Islamist militants.
US Secretary of State John Kerry said he was talking to the White House and Pentagon about the Kremlin proposal, which was made during phone calls with his Russian counterpart Sergei Lavrov in recent days.
Kerry did not offer details of the proposal but suggested it was about deconfliction - ensuring that US and Russian aircraft do not come into conflict with each other in Syria.
Both Moscow and Washington say their enemy is Islamic State, whose fighters control large parts of Syria. But Russia supports the government of President Bashar al-Assad in Syria, while the United States says Moscow's increased military presence in Syria is exacerbating violence.
"The Russians proposed ... that we have military-to-military conversation ... to discuss what precisely what will be done to deconflict with respect to any potential risks that might be run and to have a complete and clear understanding as to the road ahead and what the intentions are," Kerry told reporters.
Kerry said while the United States was still considering the proposal, he believed talks with Moscow could avert misunderstandings.
"The White House, the Defence Department and State Department are discussing next steps in order to determine the best way forward," he added.
Moscow has come under increased international pressure in recent days to explain the intentions behind its beefed-up military presence in Syria. Russia has been sending about two military cargo flights a day to an air base at Latakia, an Assad stronghold, US officials say.
Russia has deployed about 200 naval infantry soldiers to the airfield, as well as temporary housing units, a portable air traffic control station, artillery and half a dozen tanks, the officials said.
Last week Russia called for military co-operation with the United States to avert "unintended incidents."
Asked if the US military was concerned the Russian buildup could threaten coalition aircraft, Army General Lloyd Austin, the commander of US forces in the region, told a Senate hearing on Wednesday that with both sides operating in the same space "that possibility is clearly there."
Christine Wormuth, undersecretary of defence for policy, said if Russian forces began regularly conducting military flights from the base, it would be necessary to find a way to coordinate movements.
"We would, I would imagine, need to set up some sort of deconfliction mechanism so that we can continue our counter-ISIL campaign there," she said, using an acronym for the militants.
Kerry said Lavrov told him Russia was focused on fighting the Islamic State in Syria, but he added he was "not taking that at face value" because the kinds of airplanes and equipment Moscow had sent to the region raised questions.
Washington has been pressing Moscow to help with a political transition in Syria, which would see Assad hand over power to an interim governing body. But Moscow's military buildup has complicated those efforts.
Kerry said if it was true Russia was focused on fighting the Islamic State in Syria and there was a way to co-operate "then there still is a way forward to try to get to a political negotiation."