Daesh launched its fiercest assault against an Assad regime enclave in the eastern Syrian city of Deir al-Zor, reportedly cutting off the regime enclave on Monday night.

"This attack is one of the most fierce attempts by Daesh on the airport and the area," the source told Reuters, using an Arabic term for the group. "It seems Daesh has mobilized a big force," a source from Assad regime said.

The terrorist group seized from Assad forces the districts of Harabesh, Rusafa, Albunasir, Jiraiya, Meisalun, Makabes, Nishan districts, and cut off the road linking the air base controlled by Assad forces with the rest of the enclave, meaning the army is only able to supply the city with air drops. Heavy fighting has reportedly taken place around the air base and the city center.

On Monday, the Syrian Observatory for Human Rights (SOHR) said the clashes in the city had left at least 82 people dead, including Daesh terrorists, soldiers and militiamen loyal to the Assad regime, and civilians.

The oil-rich city of Deir al-Zor became a target of Daesh terrorists in 2014. The group gradually seized large swathes of the city, cornering Assad forces in an enclave located in the center of Deir al-Zor.

Daesh terrorists are currently holding the whole province of Deir al-Zor, with the exception of pockets in the city center controlled by the Assad regime. Last month it recaptured the city of Palmyra, 185 km (115 miles) southwest of Deir al-Zor, from Assad forces in an unexpected advance that demonstrated its continuing military threat.

The U.N.'s World Food Program has temporarily suspended air drops of vital supplies to the eastern Syrian city of Deir al-Zor due to heavy fighting there, a spokeswoman said yesterday. The WFP, whose last drop there was on Sunday, has carried out 177 air drops for 110,000 people in the city since beginning the operation, spokeswoman Bettina Luescher said.

We have put on hold the air drop operation in the city for security operational reasons," she said speaking to reporters in Geneva. "There is heavy fighting ongoing in and around the landing zone... It is simply too dangerous to do this now."

The WFP has been dropping humanitarian aid into Deir al-Zor since April 2016, and the government-held area is the only place in Syria where the agency has permission for the drops. The Daesh 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 regime's ability to bring in supplies and military reinforcements.

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