Beirut: Daesh fighters stormed parts of a sprawling army air base on Saturday in eastern Syria after days of clashes that killed dozens on both sides, activists said.

The sprawling base, outside the city of Deir Al Zor, has been used by the government in the past months to launch air raids on areas held by the Daesh group bordering Iraq.

The Daesh group is trying to capture the air base and a nearby barracks known as Brigade 137 to eliminate the main pocket of resistance in the area and provide a major morale and propaganda boost after a string of setbacks in recent weeks.

The Britain-based Syrian Observatory for Human Rights said the latest attack began on Saturday with a suicide car bomb attack at the main entrance of the Deir Al Zor air base. The Daesh group began a major offensive on the air base, one of the last government-held areas in the province of Deir Al Zor, on Thursday.

The Observatory said that since Thursday, 111 fighters on both sides have been killed, including 51 troops and pro-government militiamen. It said some 60 Daesh group fighters have been killed, of which 25 were Syrian.

Activists who support the Daesh group posted photos on social media showing two military helicopters that they claimed were captured by the militants.

There was no immediate word from the government about Saturday’s capture of parts of the air base.

State news agency SANA said the government’s air force was taking part in the operations at the air base, adding that they destroyed a Daesh group convoy consisting of five armored vehicles and four pickup trucks mounted with heavy machine guns.

On Friday, Daesh group fighters captured the strategic village of Jafra near the air base. If militants capture the air base and Brigade 137, they could threaten government-held areas in the provincial capital of Deir Al Zor.

Meanwhile a Syrian military source said on Saturday that government forces had repelled an attack by Daesh militants on an air base in the eastern province of Deir al-Zor, one of the last remaining government stronghold in eastern Syria.

The Britain-based Syrian Observatory for Human Rights said Daesh fighters broke into the Deir Al Zor air base at dawn on Saturday but were forced to retreat. It said 119 fighters on both sides were killed.

A Syrian security source, when asked about the breach, said: “The terrorists have been unable to control the air base.” The al Qaeda offshoot Daesh has been gradually consolidating control of the oil-producing Deir Al Zor province this year. President Bashar Al Assad’s forces have held on to the local military air base and parts of the provincial capital.

The Observatory said 51 of Al Assad’s forces and 68 members of Daesh had been killed in the three-day offensive.

“Elements of the Daesh also pulled out of a mountain overlooking Deir Al Zor due to intense shelling,” the Observatory said.

State media said on Saturday that the army had killed “a number of terrorists” in al Jufra, an area close to the airport.

Daesh has been under pressure from US air strikes in Syria since September, but that has not stopped it from launching attacks on Assad’s forces and other targets to expel government forces and rival rebels.

The Twitter account of the US embassy in Syria said late on Friday that a US air strike in Deir Al Zor had hit Daesh targets: three vehicles, an excavator and a training camp.

It was unclear whether the attacks took place near the base.

Deir Al Zor borders territories in Iraq which are also controlled by Daesh. The province’s oilfields are a major source of revenue for the group.