BEIRUT (Reuters) - The Syrian Observatory for Human Rights group said scores of Syrian government forces have been killed in three days of fighting with Islamic State in the east of the country, where the jihadist group has attacked government-held areas.

Islamic State advanced against government forces on Monday near the city of Deir al-Zor after attacking the towns of Ayyash and Begayliya, the Observatory said.

The jihadist group is in control of most of Deir al-Zor province while the government is holding parts of the city, including a military airport - one of the few pockets of east Syria still held by President Bashar al-Assad.

Syrian officials could not be reached for comment on the battles or the scale of losses on its side.

The Britain-based Observatory said 120 members of the Syrian government forces and 70 Islamic State fighters had been killed in clashes since Saturday.

The official news agency SANA reported on Monday that government forces had recaptured some residential areas taken by Islamic State in Begayliya, near the city of Deir al Zor, and killed a number of fighters.

On Tuesday, Islamic State said it had made further gains against government forces near Ayyash, and had captured two military vehicles.

Deir al-Zor province links Islamic State’s de facto capital in Raqqa with territory controlled by the group in Iraq. The group made previous attempts to take over government-held areas of the city in 2015, including the airport.

The United Nations has warned that around 200,000 besieged residents in Deir al-Zor face severe food shortages.

Islamic State kidnapped at least 400 civilians during its assault on Saturday, the Observatory said.

SANA said on Sunday that at least 300 people, including women and children, had been killed during the attacks in Deir al-Zor. Reuters was unable to independently verify the reports.