BEIRUT: Syrian troops backed by Russian warplanes completely surrounded fighters of Daesh in a vast central desert region Thursday, an activist group said.

Advancing overnight, troops north and south of the Badia desert area met up and seized Jabal al-Dahek, the Britain-based Syrian Observatory for Human Rights said.

By encircling them, the government forces dealt a “strategic” blow to the Daesh militants, it said.

They have been battling for months to retake the Badia, which stretches from the country’s center to the Iraqi and Jordanian borders and has been held by Daesh since 2014.

Fighting was still raging between the two sides near Sukhneh, one of the main towns in the desert area.

The Syrian army secured Sukhneh, 50 kilometers northeast of the ancient city of Palmyra, earlier this month. It was the last major town in Homs province held by the militant group.

Victory over Daesh in the region is seen as key to the army’s hopes of retaking Deir al-Zor, the last Syrian province that remains almost completely under Daesh control.

The Syrian government holds a pocket of territory in Deir al-Zor city and a nearby military base.

Analysts say the Syrian army needs to completely eliminate Daesh from the central part of the desert before it can attack Deir al-Zor, otherwise its troops would be exposed.

According to Fabrice Balanche, an expert on Syrian geography, the regime would have more than half of the country’s territory under its control if it can drive Daesh out of the Badia. The militants have lost swaths of Syrian territory to separate campaigns being waged by government forces backed by Russia and Iran, and by the U.S.-backed Syrian Democratic Forces, which is dominated by the Kurdish YPG militia.

The SDF is currently focused on capturing Raqqa city from Daesh.

The United Nations Thursday called for a humanitarian pause to allow an estimated 20,000 trapped civilians to escape from Raqqa, and urged the U.S.-led coalition to rein in airstrikes that have caused casualties.

Amnesty International said the coalition campaign to oust Daesh from the city had killed hundreds of civilians, and those remaining face greater risk as the fight intensifies in its final stages.

“On Raqqa, our urging today ... is that they need to do whatever is possible to make it possible for people to escape Raqqa,” Jan Egeland, U.N. humanitarian adviser on Syria, told reporters in Geneva. Humanitarian pauses were agreed between the warring sides last December to allow the evacuation of civilians from then rebel-held eastern Aleppo, Egeland said.

But he added that the United Nations has no contact with Daesh fighters who have controlled Raqqa since 2014.

Egeland, referring to the SDF said: “There is heavy shelling from the surrounding and encircling SDF forces and there are constant air raids from the coalition. So the civilian casualties are large and there seems to be no real escape for these civilians.”