Syrian forces have regained full control of Palmyra, the ancient city that fell to Islamic State, a military source has said.

"After heavy fighting during the night, the army is in full control of Palmyra - both the ancient site and the residential neighbourhoods," the source said.

Palmyra's recapture marks the biggest reversal for IS since Russia's intervention in the five-year conflict.

The city, affectionately known as the "bride of the desert," used to attract tens of thousands of tourists every year.

After taking it over last May, IS demolished some of the best-known monuments at the UNESCO world heritage site.