(reuters) -- The Syrian army and allied forces captured the al-Jafra district at the edge of Deir ezzor city on the western bank of the Euphrates, the Syrian military source said. Isis militants could only escape by crossing the river.

"They have no outlet except crossing the Euphrates towards the eastern bank and fleeing towards the desert, or (the towns of) al-Bukamal and al-Mayadin," the source told Reuters.

The Syrian Observatory for Human Rights said the army and its allies had encircled Isis in the city overnight by taking al-Jafra near the air base. The militants hold nearly a third of the city, the British-based war monitoring group said.

The Syrian army pushed into Deir ezzor city this month, with the help of Russian air power and Iran-backed [forces]. The advance broke an Isis siege of an enclave there and a nearby air base that had lasted three years.

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