PALMYRA, Syria, Dec. 11 (UPI) -- Islamic State militants were fighting Sunday to retake Syria's ancient city of Palmyra after the extremists had suffered setbacks.
The Islamic State-linked Amaq news agency claimed the group had regained "full control" of Palmyra, including a 13th-century castle overlooking the city. The Britain-based Syrian Observatory for Human Rights said Syrian President Bashar al-Assad's soldiers had withdrawn to the south.
The Russian air force earlier conducted 64 airstrikes to push back the Islamic State, the defense ministry said. The Russian military said the militants advanced because the air force didn't want to cause civilian casualties by bombing residential areas.
Russia said it killed 300 militants who "actively used car bombs with suicide bombers, armored vehicles and rocket artillery." Eleven tanks and 31 vehicles were destroyed.
Rami Abdel Rahman of the Syrian Observatory said Sunday, "Despite the ongoing air raids, IS retook all of Palmyra after the Syrian army withdrew south of the city."
Islamic State extremists retook Palmyra Saturday after two days of intense fighting against government forces.
Syrian President Bashar al-Assad's forces recaptured Palmyra in March after Islamic State occupied the city for 10 months, which saw the group partly destroying Palmyra's ancient Roman temple complex.
The government had waged a major offensive against rebels in the northern city of Aleppo. The U.S.-backed offensive by the Iraqi army had been retaking Mosul from the Islamic State.
Islamic State still controls large portions of Syria, including the vast eastern desert where Palmyra is located.
On Saturday, the U.S. military announced it was sending an additional 200 Special Operations troops to northern Syria to help the mostly Kurdish force battling militants.
Palmyra is situated near large oil fields in central Syria.