Beirut: The jihadist Islamic State of Iraq and the Levant (Isil) is now in full control of all main oil and gas fields in Syria’s Deir Al Zor province, bordering Iraq, a monitoring group said.

Isil declared an “Islamic caliphate” in areas it controls in Syria and Iraq, where it is spearheading an offensive against government troops.

“Isil took control of the Tanak oil field, located in the Sheiytat desert area in the east of Deir Al Zor province,” late Thursday after rival rebels withdrew, said he Syrian Observatory for Human Rights.

Earlier that day the jihadists seized the major Al Omar oil field.

But they have still not captured the tiny Al Ward oil field which produces barely 200 barrels of oil per day and is in the hands of a local tribe, said Observatory director Rami Abdel Rahman.

The militans seized Tanak and Al Omar after rival fighters from Al Qaida’s Al Nusra Front and other Syrian rebel groups withdrew from those areas, said the Observatory.

In January, Al Nusra and other Islamist militants turned their guns on the jihadists, then known as the Islamic State of Iraq and the Levant, as they swept across Syria imposing their hegemony and brutal abuse.

The rebels expelled Isil from the northeastern Idlib province and from much of Aleppo, but the jihadist group remains firmly in control of its bastion in Raqa province.

In Deir Al Zor, Isil has taken over nearly all the countryside, its troops bolstered by heavy weapons captured from Iraqi troops fleeing an offensive spearheaded by the militants.