Syrian army soldiers drive past the Arch of Triumph in the historic city of Palmyra, in Homs Governorate, Syria in this April 1, 2016 file photo Image Credit: AFP

BEIRUT: A Russian aerial onslaught forced Daesh terrorists to withdraw from Syria's Palmyra at dawn on Sunday, only hours after they had re-entered the ancient city, a monitor said.

"Intense Russian raids since last night forced Daesh out of Palmyra, hours after they retook control of the city," said Rami Abdel Rahman of the Syrian Observatory for Human Rights monitoring group.

"Russian air force planes carried out 64 air strikes against the positions, convoys and advancing reserves of militants," a defence ministry statement said.

"Over the past night, Syrian government troops with active support of the Russian air force thwarted all terrorist attacks on Palmyra," it said.

"The attacking militants actively used car bombs with suicide bombers, armoured vehicles and rocket artillery," it said, adding that the strikes killed more than 300 militants and destroyed 11 tanks and 31 vehicles.

The raids killed a large number of terrorists in the desert city in central Syria, Abdel Rahman said, without being able to give a precise number.

"The army brought reinforcements into Palmyra last night, and the raids are continuing on terrorist positions around the city," Abdel Rahman told AFP.

Daesh began an offensive just days ago near Palmyra, which is on UNESCO's World Heritage list.

In May last year, the extremist group seized several towns in Homs province including Palmyra, where they caused extensive damage to many of its ancient sites.

They were ousted from Palmyra in March by Syrian regime forces backed by Russia.