A defiant Russia yesterday said it was ready to increase military support to Syria's Bashar al-Assad if needed, dismissing suggestions it could hamper Western efforts to fight Islamic State militants.
Washington has accused Moscow of solidifying its foothold in Syria, raising concerns it could throw a wrench in plans by the US-led coalition to step up operations against jihadists in the war-torn country.
The fresh tension erupted just weeks before the UN General Assembly in New York at which Russian President Vladimir Putin is scheduled to speak.
Speaking to reporters, Foreign Minister Sergei Lavrov said Moscow wanted to avoid a repeat of the "Libyan scenario" in Syria and would therefore provide greater military assistance to the Syrian president if requested.
"We helped, are continuing to help and will help the Syrian government when it comes to supplying the Syrian army with everything it needs," he said.
But he denied that Moscow was ramping up its military presence in Syria, saying Russia was merely supplying its ally with humanitarian aid and military equipment in accordance with existing contracts.
"Russian is sending planes to Syria with both military equipment in accordance with current contracts and humanitarian aid," he said.
"We have never made our military presence (in Syria) a secret," he said. "Russia is not taking any additional steps."
US officials said this week that Russia had been sending ships, armoured personnel carriers and naval infantry to Syria in an apparent effort to prop up the besieged regime.
The White House warned this week that a Russian military buildup in Syria could spark a "confrontation" with US-led forces carrying out an air campaign against the ISIS group.
Lavrov said he had discussed Washington's concerns with US Secretary of State John Kerry who had phoned him twice over the past few days.
Putin has called for the establishment of a wider coalition to combat ISIS in Syria and his spokesman said he would raise the issue in his UN address.