US-BACKED Free Syrian Army insurgents have pleaded with the United Nations to save them from a Syrian army offensive.

The rebel forces issued a statement yesterday urging the UN to put pressure on Russia to stop supporting “Assad government militia.”

That came as a new push by the Syrian army and its allies threatened to cut off a rebel-held pocket in south-eastern Rif Dimashq and Sweida provinces and surround the militants.

Later, anti-government forces claimed to have shot down a Syrian warplane.

US, British and Norwegian troops occupying the isolated Tanf border crossing to the east have not moved to save the militants, despite having previously supported their bid to seize eastern Deir Ezzor province.

Meanwhile, the Kurdish-led Syrian Democratic Forces, which receive US aid, advanced on Deir Ezzor from the north-west, capturing the town of al-Ukayrshi, south-east of besieged Raqqa, from Isis.

Further south, the army took full control of the al-Hayl gas field east of Palmyra from the extremist group.

Yesterday, the Coventry-based Syrian Observatory of Human Rights said its contacts in Deir Ezzor had confirmation of the death of Isis leader Abu Bakr al-Baghdadi “somewhere near the Iraqi border” from leaders of the terrorist army.

Earlier Iraq’s al -Sumaria television quoted a source in Nineveh province as saying that Isis had announced his death and appointed a “new caliph.”

The Russian Defence Ministry said last month that it was confident Mr Baghdadi had been killed in a May air strike on an Isis war council meeting in Raqqa.