Russia said on Thursday it ships both humanitarian aid and military equipment to Syria by air, at a time when Washington is putting pressure on nearby states to deny their airspace to Russian flights.
Moscow has come under increased international pressure in recent days over what Washington and Gulf states say is Russian military build-up in Syria, where the Kremlin has helped buttress its longtime ally President Bashar Assad in 4 1/2 years of war.
Reuters reported this week that Lebanese sources believe Russian troops have begun participating in combat operations in Syria and are setting up new bases there. U.S officials say Russian combat troops and equipment have been arriving by both air and sea.
Russia complained after Bulgaria denied its airspace to Syrian-bound Russian flights. Sofia said future flights would be allowed only if they had their cargoes inspected.
Moscow has long acknowledged it sells weapons to the Syrian government under long-standing agreements. Foreign Minister Sergei Lavrov said on Thursday that some of those arms are shipped by air.
"Russia sends both military production, in line with existing contracts, and humanitarian aid on planes going to Syria," Foreign Minister Sergei Lavrov said on Thursday.
Moscow says all its military assistance to the Syrian army is in line with international law and that its servicemen, including military experts, have been present inside Syria for many years.
Russian officials have not commented directly on the reports that Russian troops have taken part in combat. Moscow says Assad's government should be part of international efforts to combat Islamist militants, including the Islamic State group.
"The threat coming from Islamic State is evident … The only force capable of resisting it is the Syrian armed forces," Kremlin spokesman Dmitry Peskov told journalists.
The United States and its allies are leading an air war against the Islamic State but also oppose Assad, whose government has been fighting an array of insurgent groups. Around 250,000 people have died and half of Syria's 23 million people have been driven from their homes by the multi-sided civil war.
Government forces have faced major setbacks on the battlefield this year. Russia's only naval base in the Mediterranean Sea is at Tartus on Syria's coast, and protecting it would be a major strategic objective for Moscow.
Peskov said Putin would talk about Syria and fighting the Islamic State during a speech to the UN General Assembly in New York later this month. He said no meeting with U.S. President Barack Obama there was currently scheduled.
Russia's respected Kommersant daily on Thursday said Moscow's advanced BTR-82A armored personnel carriers were among arms supplied to Damascus.