Russian Foreign Minister Sergei Lavrov discussed the Syrian conflict with his American counterpart, Secretary of State John Kerry, for the second time in four days Wednesday, AFP reported.

The phone call came amid concerns in Washington over an alleged Russian military buildup in the war-torn country.

The two discussed “the problems of regulating the conflict in Syria,” the foreign ministry in Moscow said in a terse statement, without providing further details.

The New York Times reported late last week 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.

That report was followed up by new images which came to light and which appeared to confirm previous reports of Russian “boots on the ground” in Syria.

And, American officials on Tuesday said three Russian military transport planes had landed in Syria in recent days, and that new housing units had been set up at the airport in the port city of Latakia, suggesting a possible increase in Russia’s military support for embattled President Bashar Al-Assad’s regime.

The first telephone conversation between Kerry and Lavrov took place on Saturday, and he expressed his concern about the reports of the increased presence in Syria.

Moscow, however, said on Monday that the aid it provides to Damascus is normal.

Syria on Tuesday also denied the reports of increased military activity by Russian troops on its soil, with Syria’s Information Minister Omran Zohbi dismissing the reports as “baseless”.

“There is absolutely nothing to these rumors and what was said a few days ago,” Zohbi said, adding, “There are no Russian forces, and there is no Russian military activity on Syrian territory by land, sea or air.”