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. </s> Children walk at a camp for displaced people who fled fighting in the Daesh stronghold of Raqqa, in Ain Issa, Syria, on Friday (Reuters file photo)

BEIRUT — The Syrian army backed by heavy Russian air strikes seized a string of oil wells in southwest Raqqa province on Saturday, as retreating the Daesh terror group militants battle to defend their remaining territory in the country.

State-owned Ikhbariyah television quoted a military source as saying the army had 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.

The seized oil fields lie south of the town of Rasafa and its oil wells, which the army took last month from the militants in their first major territorial gains inside the province.

The army and Iranian-backed militias have in the last few months been advancing east of Aleppo city and seizing swathes of territory west of the Euphrates River that militants have pulled out of to defend their de facto capital of Raqqa, where they are now battling US-backed troops inside the city.

The latest gains tighten the army's grip on a bulge of territory stretching from eastern Hama province to eastern Homs and the edge of Raqqa and Deir Ezzor provinces, the Syrian Observatory for Human Rights war monitor said.

The monitor said the Russian air force intensified its strikes on several targets and towns held by the militants in the area including Uqairbat, a target of Russian cruise missiles fired from warships in the Mediterranean at the end of May.

The army's next goal is to retake the town of Sukhna, a gateway to the eastern province of Deir Ezzor that borders Iraq and likely to be the militants' last major bastion in Syria if Raqqa falls.

The army and its Iranian-backed allies have also announced in the last few days steady gains in the desert northeast of the ancient city of Palmyra with their capture of the Hail gas field that brought them almost 18km south of Sukhna.

Heavy fighting has ‘however’ continued in the last 48 hours near Hail and the nearby Arak gas field that the Syrian army took last month, both the Syrian Observatory for Human Rights and extremist websites said.

The army and Iranian-backed militias have been engaged in a campaign since May to fill the void left by the retreat of militants in areas they once controlled in the vast eastern Syrian desert that stretches all the way from central Syria to the south eastern border with Iraq and Jordan.

In the southeastern desert, heavy fighting continued between the army and its Iranian backed allies on one side and the Western-backed Free Syrian Army (FSA) rebels in the rugged eastern countryside of the city of Sweida in southern Syria.

The army said it had captured most of these areas that are also near the border with Jordan, while the rebels said they had inflicted losses on Lebanon’s powerful Hizbollah group and Iraqi Shiite militias. </s> The UK-based Syrian Observatory for Human rights said the militants had entered Palmyra after they had taken strategic heights near the city and captured the northern part of the city and mountains around it.

The Syrian army earlier said it had sent reinforcements to Palmyra, to help the army defend the city in what some rebels said were coming from Aleppo and forcing the Syrian government to divert troops from the city where the army and Iranian backed militias were on the verge of a major victory against rebels.

A statement by Islamic State's news agency Amaq said the group had taken the strategic Jabal al Tar and Jabal Antara mountains that overlook the city in some of the heaviest fighting since the group lost the city.

The militants were pushing towards the T4 airbase, one of Syria's major military bases, near Palmyra city and which Russian forces have been using to support the Syrian army.

Islamic State's assault, which began late on Thursday, has killed dozens of Syrian soldiers and quickly taken over grain silos and control of some oil and gas fields around Palmyra, monitoring group the Syrian Observatory for Human Rights said.

The U.S.-led coalition which is separately fighting the militants said late on Friday it had taken out 168 IS oil tanker trucks near Palmyra in a large air raid.
The SOHR and Amaq announce that ISIL has captured an oil field north-west of Palmyra.