IS fighters 're-enter historic city of Palmyra'

Islamic State fighters have re-entered the historic city of Palmyra for the first time since they were expelled by government and Russian forces nine months ago.

Activists said militants had nearly encircled the city and entered its northern and northwestern neighbourhoods.

IS fighters are also approaching the city's UNESCO heritage site, the Palmyra Coordination network said.

Osama al-Khatib said government soldiers were fleeing the city.

"The army as an institution has dissolved," he said.

"Some soldiers and militiamen remain in the city, along with 120 families who have not been able to leave.

"There is strong fighting on all sides. There is no exit except through a corridor to the west."

The dramatic reversal in Palmyra comes days after IS militants in the Iraqi city of Mosul launched a major counterattack that surprised Iraqi soldiers, killing at least 20 and halting their advance.

Iraqi special forces units have entered the eastern outskirts of the largest remaining IS-held city.

But their advance has been greatly slowed by both a desire to limit civilian casualties and the resilience of the IS fighters.

British-based Syrian Observatory for Human Rights said the militants reached the city's Tadmor Hospital and its strategically located wheat silos.

IS destroyed several of the city's famed ancient Roman monuments and executed its archaeological director after sweeping into the city in July 2015 and holding it for 11 months.