The World Food Programme said Tuesday it has suspended aid drops to the Syrian city of Deir Ezzor because of heavy fighting after a fierce assault by the Islamic State group.

IS has besieged Deir Ezzor's 100,000 residents since 2015 and already controls large parts of the city, but on Saturday advanced further inside remaining government-held territory.

The clashes, which continued for a fourth day on Tuesday, have killed more than 100 people, according to a monitor.

"We have put on hold the air drop operation in Deir Ezzor for security operational reasons," said WFP spokeswoman Bettina Luescher.

"There is heavy fighting ongoing in and around the landing zone... It is simply too dangerous to do this now," she told reports in Geneva.

The WFP has been dropping humanitarian aid into Deir Ezzor since April 2016, and the government-held area is the only place in Syria where the agency has permission for the drops.

Luescher said the WFP's last aid drop was on Sunday, adding that 3,300 tonnes of food and other aid have been dispatched to the city since the operation began.

The IS assault has managed to divide the east of the remaining government-held parts of the city from the west.

It has also cut the route running from the city's key military airport, limiting the government's ability to bring in supplies and military reinforcements.

The Britain-based Syrian Observatory for Human Rights monitor said Tuesday that Syria's military and allied Russian forces were carrying out air strikes against IS, as government troops battled the jihadists on the ground.

Ten civilians were killed Tuesday in air strikes on the Deir Ezzor district of Al-Ummal, which is held by IS, the monitor said, bringing to 37 the total number of civilians killed in the four-day IS offensive.

The latest assault, which included waves of suicide bombers, was the "most violent" attack on the city in more than a year, said the Observatory.

It said the government was flying reinforcements into the military base and had called up residents to fight on the front lines against IS, including some without military training.

Since the siege began, the government has been able to fly limited supplies into the airport, and WFP and Russia have also delivered aid.

But residents have nonetheless faced shortages and rising prices, as well as being unable to leave the city.

Deir Ezzor sits in the oil-rich eastern province of the same name, most of which is controlled by IS.

The extremist group has lost swathes of territory in northern Syria to Kurdish fighters as well as a Turkish-backed rebel alliance, but it remains on the offensive in other parts of the country.

More than 310,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests that were met with a regime crackdown.

The violence has drawn in international players, as well as attracting jihadist groups like IS.

Source :AFP