BEIRUT — In a move that could reverberate across the Middle East, Iran confirmed Wednesday that Russia is using its territory to launch airstrikes in Syria even as a second wave of Moscow’s bombers flew out of the Islamic Republic to hit targets in the war-ravaged country.

The development represents a historical rapprochement with Russia that could rile U.S.-allied Gulf neighbors, strengthen Syrian President Bashar Assad and affect the war against the Islamic State group

Russia first announced the strikes on Tuesday from near the Iranian city of Hamedan, 175 miles southwest of the Iranian capital, Tehran. On Wednesday, Russia’s Defense Ministry said another wave of warplanes had departed from Iran, striking targets in eastern Syria.

In Moscow, Russian Foreign Minister Sergey Lavrov defended the use of Iranian military bases for airstrikes in Syria, rejecting allegations that it could be a violation of U.N. resolutions prohibiting the supply, sale and transfer of combat aircraft to Iran.

“The Russian air force uses these warplanes with Iran’s approval in order to take part in the counter-terrorism operation” in Syria, he said.

In Washington, State Department spokesman Mark Toner said Russia was “exacerbating what is already a very dangerous situation … by using Iranian air bases as a way to carry out more intensive bombing runs that continue to hit civilian populations.”