Does Russia’s use of Iran airbases for Syria strikes breach sanctions?

The US Department of State has suggested that Russia’s use of Iranian military airbases to launch strikes in Syria could violate UN sanctions on Iran which prohibit the supply, sale, and transfer of military aircraft to Iran unless approved by the UN Security Council. Russia’s Foreign Minister Sergey Lavrov has denied this allegation, saying yesterday that “there has been no supply, sale, or transfer of fighter jets to Iran… The Russian Air Force uses these fighter jets with Iran’s approval”.