Russia's Foreign Minister Sergey Lavrov confirmed on Thursday that the country's humanitarian aid flights to Syria carry military equipment as well — after the United States and NATO warned Moscow over its involvement in the Syrian conflict.
"Russian planes are sending to Syria both military equipment in accordance with current contracts and humanitarian aid," he told reporters.
According to Russia's Kommersant daily newspaper said earlier Thursday that Moscow's advanced BTR-82A armored personnel carriers were among equipment supplied to Damascus.
Moscow previously insisted that its flights to Syria were only for humanitarian purposes. But Israel on Thursday added to claims that Russia has sent an active military force to Syria with the purpose of setting up an air base.
"As far as we understand, at this stage we are talking about a limited force that includes advisers, a security team and preparations for operating planes and combat helicopters," Israel's Defense Minister Moshe Yaalon said during a press briefing.
The Kremlin declined to comment Thursday on whether Russian troops were fighting in Syria, after sources in Lebanon told Reuters that Russian forces began participating in military operations.
"The threat coming from Islamic State is evident ... The only force capable of resisting it is the Syrian armed forces," said Kremlin spokesman Dmitry Peskov, reiterating Russia's position that its longtime ally Syrian President Bashar al-Assad should be part of international efforts to combat the Islamic State in Iraq and the Levant, also referred to as ISIL and the Islamic State.
Washington has put pressure on Greece and Bulgaria in recent days to deny Russia's requests to use their airspace for its Syria flights.
During a news conference with the Slovakian prime minister, Ukrainian Prime Minister Arseny Yatsenyuk announced that the country will close its airspace to Russian planes flying to Syria.
On Wednesday, U.S. Secretary of State John Kerry expressed concern over reports of Russian military activities in Syria, warning that it could fan more violence, a State Department spokesman said.
Aerial imagery indicated that Russia is focusing on Bassel al-Assad International Airport, south of Latakia on Syria's Mediterranean coast, and on the Russian naval facility in Tartus, Agence France-Presse reported.
Jens Stoltenberg, NATO's secretary-general, echoed Kerry’s concerns, saying the move "will not contribute to solving the conflict … I think it is important to now support all efforts to find a political solution to the conflict in Syria. We support very much the efforts by the U.N."
One U.S. official, who was not authorized to comment publicly and asked not to be identified, told AFP that two tank-landing ships recently arrived at Tartus and that about a dozen Russian armored personnel carriers are at Bassel al-Assad Airport, which is named after the president's older brother.
The official said that dozens of Russian naval infantry troops have arrived in Syria and that their role was likely to protect incoming military hardware rather than engage in combat.
In addition, a giant Antonov-124 Condor military transporter has flown to the airport, bringing the number of transport flights to at least four in recent days.
The developments further complicate the deadly crisis in Syria, where the conflict has claimed nearly 250,000 lives since 2011 and triggered a massive outflow of refugees, many of whom are fleeing to Europe.
Mamoun Abu Nowar, a retired Jordanian air force general, told Al Jazeera on Thursday that Russia is sending fighter jets to support the Syrian military.
"It is clearly obvious that Assad's forces have faced setbacks. So this Russian movement sends a great signal that Assad must not go," he said, adding that an estimated 1,000 prefabricated houses have been built in Syria to accommodate Russian troops.
Al Jazeera and wire services