Washington accused Moscow of assembling a strike force at a Syrian government stronghold to assist embattled President Bashar Assad in his war against various extremist groups.
"Last time I looked, ISIL [Islamic State] is not flying any aircraft," Kirby said. "So the fact that you have fighter aircraft, air-to-air capabilities brings up legitimate question. Because they don’t have aircraft, the need to have surface-to-air missile capability is a little bit quizzical."
Earlier in September, Russian President Vladimir Putin confirmed that Moscow was providing considerable support to Syria in terms of equipment, weapons and training to fight the Islamic State and other terrorist groups.
"Some of that, I think you could reasonably argue, could be effective against terrorists. Some of that is a little less clear. So, I think we continue to have legitimate concerns and questions about Russia’s overall intent here," Kirby said.
The Obama administration has been critical of Russia’s support for Syrian President Bashar Assad in the fight against the Islamic State. Moscow, however, has urged the US-led coalition against the Islamic State to join forces with the Syrian government in its fight against the terrorist group.
Syria has been mired in civil war since 2011, with opposition factions and Islamic extremist groups, including the Islamic State and the Nusra Front, fighting the Syrian Army.
