Syrian troops and allied militia pressed a major advance against militants in Palmyra on Friday, coming within several hundred metres (yards) of the ancient city's famed ruins, the country's antiquities chief told AFP.

Palmyra, known as the "Pearl of the Desert", was overrun by the Islamic State group (IS) last May, causing global concern. The group has since blown up UNESCO-listed temples and looted relics that dated back thousands of years.

"In the southwest, the army has liberated the district of hotels and restaurants as well as the Valley of the Tombs," Maamoun Abdelkarim said.

"And in the west, the army has taken the Syriatel hilltop that overlooks the Mamluk fort built in the 13th century, which is still under IS group control," he added.

State television aired live footage showing air strikes targeting positions near the fort.

"The army is now 600 metres from the Temple of Bel, but it is advancing slowly because of mines and above all to protect the city, which is an ancient treasure," Abdelkarim said.

IS group claimed in September to have destroyed the Temple of Bel, which UNESCO described as one of the best preserved and most important first century religious edifices in the Middle East.

A military source confirmed the advance, adding that a sandstorm that began Thursday evening also reduced visibility.

The army and pro-regime militia entered Palmyra on Thursday, weeks after launching an offensive backed by Syrian and Russian warplanes earlier in March.

Palmyra's recapture would be a major strategic and symbolic victory for Assad, since whoever holds it also controls the vast desert extending from central Syria to the Iraqi border.