US-BACKED Syrian forces seized the country’s largest oil field near the Iraqi border from Isis yesterday after the extremists allegedly switched sides, giving up the fields without a fight.

The Syrian Democratic Forces (SDF) — a predominantly Kurdish group which last week declared the “total liberation” of Isis’s former stronghold of Raqqa — said it had taken the al-Omar oil field northeast of Deir Ezzor in a “swift and wide military operation.”

But Lebanon’s Al-Masdar News claimed local militia who had pledged allegiance to Isis in 2014 had defected to the SDF, handing them the lucrative resource without a fight.