Russia has sent fighter jets to Syria, US officials said, raising the stakes in a military buildup that has put Washington on edge and led to the first talks between US and Russian defence chiefs in over a year, Guardian reported.
US defence secretary Ash Carter, concerned over the possibility of rival US and Russian air operations in Syria's limited airspace, agreed in a call with his Russian counterpart to explore ways to avoid accidental military interactions.
The coordination necessary to avoid such encounters is known in military parlance as "deconfliction".
"They agreed to further discuss mechanisms for deconfliction in Syria and the counter-Isil campaign," Pentagon spokesman Peter Cook said after the call, referring to the campaign by the United States and its allies against Islamic State (Isis) militants.
The two countries have a common adversary in Isis militants in Syria, even as Washington opposes Moscow's support for Syrian president Bashar al-Assad, seeing him as a driver of the nation's devastating, four-and-a-half-year civil war.
A senior US defence official, recounting details of the conversation, said Russia's defence minister, Sergei Shoigu, had described Moscow's activities in Syria as defensive in nature.
Shoigu said Russia's military moves "were designed to honor commitments made to the Syrian government", the US official said. It was unclear, however, what those commitments to Syria are or how Russia's military buildup was relevant to them.
The talks between Russia and the US came as Syrian army jets carried out at least 25 air strikes on the Isis-held city of Palmyra on Friday, one of the most sustained government bombardments of the city, the Syrian Observatory for Human Rights said. The air strikes killed at least 26 people, including 12 Isis fighters, the Britain-based Observatory said.