Islamic State (Isis) forces seized Syria’s al-Tanak oilfield in the eastern province of Deir el-Zour yesterday as they sought to extend their control along the Euphrates river.

The extremist group had taken control of the country’s largest oilfield, al-Omar, on Thursday.

Rival jihadist group the Al-Nusra Front had boasted of controlling both installations, but the group’s fighters melted away in the face of the Isis offensive.

The victories mean that Isis has expanded the area under its control along the border with Iraq, allowing its forces to move freely between the two countries.

Islamic State fighters have also been pushing strongly northwards up the Euphrates river toward Turkey over the past three days, shelling the town of Akhtarin just 11 miles from the border yesterday.

However, government troops strengthened their position near Aleppo, taking control of an industrial area that will enable them to more easily blockade rebel-held eastern parts of the city.