The Islamic State (IS) militant group has destroyed part of what's considered the most important temple at the ancient Syrian site of Palmyra, activists and witnesses say.

The extent of the damage to the 2,000-year-old Temple of Bel is not clear but local residents have described being shaken by a large explosion.

The reports come a week after IS blew up another temple at the ancient city.

The militants seized control of Palmyra in May, sparking fears for the site.

The world-famous Greco-Roman ruins are in the desert north-east of the Syrian capital, Damascus.

"It is total destruction,'' one Palmyra resident told the Associated Press news agency. "The bricks and columns are on the ground."

"It was an explosion the deaf would hear," he went on, adding that only the wall of the temple remains.

The temple was dedicated to the Palmyrene gods and was one of the best preserved parts of the site.

It was several days after the initial reports of the destruction of another part of the site, the Temple of Baalshamin, that IS itself put out pictures showing its militants blowing up the temple.

The BBC's Jim Muir, in Beirut, says that for the extremists, any representation implying the existence of a god other than theirs is sacrilege and idolatry.

The modern city of Palmyra - known locally as Tadmur - is situated in a strategically important area on the road between the Syrian capital, Damascus, and the eastern city of Deir al-Zour.

The ancient city was a major cultural centre and is a Unesco World Heritage site.

Unesco has condemned the deliberate destruction of Syria's cultural heritage as a war crime.

IS has used Palmyra's theatre to stage the public execution by children of more than 20 captured Syrian army soldiers.

The group has ransacked and demolished several similar sites in the parts of neighbouring Iraq which they overran last year, destroying priceless ancient artefacts.

Ancient city of Palmyra

• Unesco World Heritage site

• Site contains monumental ruins of great city, once one of the most important cultural centres of the ancient world

• Art and architecture, from the 1st and 2nd Centuries, combine Greco-Roman techniques with local traditions and Persian influences

• Site boasts a number of monumental projects, more than 1,000 columns, and a formidable necropolis of more than 500 tombs

• More than 150,000 tourists visited Palmyra every year before the Syrian conflict