Russia has said that its use of an Iranian airbase to conduct bombing missions in Syria does not violate a UN resolution that forbids supplying warplanes to Tehran.
"No supplying, selling or transferring of warplanes to Iran has occurred," Russian Foreign Minister Sergei Lavrov said Wednesday in comments carried by state news agency TASS.
US State Department spokesman Mark Toner on Tuesday said that Russia might be violating UN Security Council Resolution 2231 by using Iranian territory to launch airstrikes in Syria.
The resolution prohibits the supply, sale or transfer of combat aircraft to Iran unless approved in advanced by the UN Security Council.
Toner also described Russia's move as "unfortunate but not surprising or unexpected," saying the airstrikes that purport to target Islamic State in Syria "predominately target moderate Syrian opposition forces."
Meanwhile, the speaker of Iran's parliament, Ali Larijani, denied that Russian warplanes had been using Iranian territory.
"We have made no airbase available to Russia or any other country," Larijani told parliament, according to Iran's IRNA news agency.
However, he added that Russia is an important ally and has had close cooperation with Iran regarding the Syria conflict.
The Defence Ministry in Moscow said Wednesday that Russian Su-34 warplanes took off from an airbase in Iran and conducted an airstrike against Islamic State in the Syrian province of Deir al-Zour.
The attack hit two Islamic State command points and large training camps, "eliminating more than 150 militants," the ministry said in comments carried by TASS.
On Tuesday, Russian warplanes used an Iranian airbase for the first time for military actions in Syria, TASS reported.
The airbase, in Iran's western Hamadan region, is much closer to Islamic State targets than the Khmeimim airbase, which Russia had previously been using, in coastal northern Syria.
Russia and Iran are longtime allies of Syrian President Bashar al-Assad, and Moscow and Washington support opposing sides in Syria.