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BEIRUT (Reuters) - The Syrian army supported by Iranian backed militias seized new oil fields in the desert in the southwest of Raqqa province on Monday in new advances against retreating Islamic state militants.

The Syrian army said on state media they had taken al Daylaa oil field alongside the Zamla gas field in large stretches of territory the militant group have been pulling out of in recent weeks to defend their remaining possessions in Syria.

On Saturday the army said they taken control of Wahab, al Fahd, Dbaysan, al-Qseer, Abu al Qatat and Abu Qatash oil fields and several other villages in the desert area that lies in the southwest of Raqqa province.

Most of Syria’s oil fields are mainly located in the northeastern province of Hasaka which is the hands of Kurdish YPG militia and also in Raqqa province where the militants have been losing large swathes of territory to advancing U.S. backed forces now battling them inside Raqqa city.

The Syrian Observatory for Human Rights said the Syrian army, supported by Iranian-backed militias from Iraq and Lebanon, was now on the edge of the Bushra chain of mountains, a main militant hideout 55 km west of Deir Zor city.

State media said Russian jets also bombed the area around Sukhna town further south, which is the gateway to the eastern province of Deir al-Zor that borders Iraq and likely to be the militants’ last major bastion in Syria if Raqqa falls.

The army’s capture last week of the major Hail gas field northeast of the ancient city brought them 18 kms to the south of Sukhna.

On Monday, an army statement said they had captured key areas west of Sukhna and killed scores of Islamic State militants as they steadily advanced towards the town whose capture would ease the path towards Deir al Zor.