The Russian military says it has teamed up with Turkey to conduct joint airstrikes against an Islamic State group's stronghold in northern Syria.

Lt. Gen. Sergei Rudskoi of the military's General Staff said nine Russian warplanes and eight Turkish jets have taken part in the strikes on the outskirts of al-Bab in the province of Aleppo.

Rudskoi's statement on Wednesday was the first acknowledgement of the Russian strikes in support of the Turkish offensive on al-Bab.

It highlighted an increasingly close alliance between Russia and Turkey, which last month jointly brokered a Syria truce and are working to prepare Syrian talks in Kazakhstan next week.

The two nations have backed opposing sides in the nearly six-year Syrian conflict, with Moscow supporting Syrian President Bashar Assad and Ankara backing his foes.