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

The extent of the damage to the two thousand-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.

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

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