Secretary of State John Kerry
Secretary of State John KerryThinkstock

Secretary of State John Kerry on Tuesday night made his third phone call to his Russian counterpart in the last 10 days, a State Department official said, according to The Associated Press (AP).

This phone call as well sought to clarify the intent of Moscow’s military buildup in Syria, and warned that continued support for President Bashar Al-Assad will only prolong the Syrian conflict, the report said.

State Department spokesman John Kirby said Kerry called Foreign Minister Sergei Lavrov on Tuesday. Another official, speaking on condition of anonymity, said the call was about Syria.

Recent reports indicated that Russia had sent a military advance team to its ally Syria and was taking other steps that Washington fears may signal plans to vastly expand military support for the beleaguered Assad.

New images later came to light which appeared to confirm previous reports of Russian "boots on the ground" in Syria.

Following the reports, a concerned Kerry phoned his Russian counterpart, following which Moscow claimed that the aid it provides to Damascus is normal.

This was followed by a second phone call between Kerry and Lavrov, in which the two discussed "the problems of regulating the conflict in Syria".

Kerry’s latest call to Lavrov came shortly after Russian President Vladimir Putin defended his military assistance to Assad’s government, according to AP. Putin said it is impossible to defeat the Islamic State group without cooperating with Damascus and urged other countries to join the cause.

Putin’s comments came after Lavrov reiterated that Russia will support the Syrian government in the fight against ISIS, saying that excluding the Syrian army from the fight against ISIS is “absurd”.

At the White House, spokesman Josh Earnest told reporters that President Barack Obama might reach out to Putin in the coming days and would not rule out a meeting of the two leaders later this month at the United Nations General Assembly.

Earnest said the administration’s stance on Russia’s moves in Syria remains the same as it was last week when Obama told U.S. troops that a strategy to prop up Assad is “doomed to failure.”

“We’ve made clear that further support, military or otherwise for the Assad regime is destabilizing and counterproductive, principally because Assad has lost the legitimacy to lead that country,” he said, according to AP, and added, “Russia’s decision to double down on Assad is a losing bet.”