SYRIA’S army made lightning advances against Isis yesterday, threatening to leapfrog the US-backed Kurdish-led Syrian Democratic Forces (SDF) south of Raqqa.

Troops pushed 15 miles south-east from recently taken areas on the Euphrates river to Bir Nabaj and reached the Ithriyah road, south of the Tabqah dam, which is held by the SDF. Later reports said the army had taken the ar-Rusafa road junction south of Tabqa.

But it was unclear whether the government forces’ plan was to strike east towards the town of al-Rusafa itself, west into Hama province to surround a large pocket of Isis territory or south towards Palmyra to join the offensive towards al-Sukhnah.

Early reports from west of Palmyra claimed troops had taken the town of Arak and its gas fields, the last major settlement before al-Sukhnah on the road to the Isis-besieged city of Deir Ezzor, the army’s main objective. But the Syrian Ministry of Defence said only that some 40 square miles of territory south and north-east of Palmyra had been taken.

Isis launched a last-ditch bid to take Deir Ezzor this month in the face of the SDF offensive on Raqqa, Isis’s Syrian “capital.” Yesterday Deir Ezzor’s defenders beat off fierce assaults as Russian planes dropped 20 tons of humanitarian aid.

On Friday the commander of Russian ground forces in Syria, Colonel General Sergey Surovikin, accused the US and SDF of allowing Isis terrorists to escape Raqqa and join the Deir Ezzor offensive.

In Raqqa the SDF said yesterday it had added the western Hattin industrial district and the outlying village of Suheil to the 17th Division army base and nearby sugar factory to the north-east, which it took on Monday.