Russian jets struck an opposition held town in southwest Syria on Sunday, opposition sources said, in the first air cover provided by Moscow to an expanding Syrian army offensive to recapture the strategic area bordering Jordan and the Israeli occupied Golan Heights.

Two tracking centers that monitor military aircraft movements recorded at least twenty strikes on Busra al-Harir, northeast of Deraa, a city in Syria, two sources told Reuters.

"We have tracked a sortie of 5 Russian jets that performed 25 raids," said one source saying the war jets had set off from Russia's Hmeimim air base in the western coastal province of Latakia in Syria.