Russian jets have started bombing the area around the Isis-held city of Palmyra.
"Su-25 jets hit a fortified IS position in the Tadmur area of Homs province," Moscow's defence ministry said in a statement reported by Yahoo News, using the Arabic name for Palmyra.
"As a result of a direct strike a fortification, underground bunker and anti-aircraft artillery were destroyed."
Russia's air force flew 131 sorties and hit 237 targets in Syria in the last two days, the ministry went on to say.
Isis have previously destroyed two ancient templates and several tower tombs at the UNESCO World Heritage site of Palmyra.
The Islamist militants destroyed various iconic religious buildings which had survived for 2,000 years as they sought to remove any form of idolatry.
They went on to behead 81-year-old Khaled al-Asaad, the archaeological director of a museum detailing Palmyra's antiquities.
