The US Secretary of State, John Kerry, has warned Russian Foreign Minister Sergey Lavrov that the alleged Russian military build-up in Syria could escalate the conflict.

The US Secretary of State, John Kerry, has warned Russian Foreign Minister Sergey Lavrov that the alleged Russian military build-up in Syria could escalate the conflict, the US State Department said in a statement Saturday.

"The secretary called Russian Foreign Minister Lavrov this morning to discuss Syria, including US concerns about the reports suggesting an imminent enhanced Russian military build-up there," the statement said.

According to media reports, Russian jets and unmanned aircrafts were allegedly flying over Syria to provide intelligence for the Syrian national forces; moreover there were allegations about Moscow's plans to build a military base inside Syria.

According to the statement, Kerry told Lavrov that if such reports were correct then it would escalate the conflict in the region.

The two leaders agreed to discuss Syria in New York during the UN General Assembly meetings late September.

More than 220,000 people have been killed since the Syria war began in 2011 and around seven million people have become refugees since then.