Islamic State drew a significant number of pro-Syrian regime troops into a protracted engagement in the country’s Badia desert over the past week, killing several of them, a number of sources reported.

The group “besieged” two units of some 500 fighters near the town of Sukhnah, resulting in a number of dead and wounded, the pro-regime Liwa’ al-Quds (the Jerusalem Brigade) militia claimed on its Facebook page on Friday.

According to the statement, the encircled force had been sent out to search for members of the Syrian Arab Army’s 18th Division “who had been lost in the Syrian desert in the village of al-Kom in the area of Sukhnah” in another attack days prior.

ISIS claimed responsibility for both attacks through its Amaq propaganda agency.

The jihadist group claimed to have killed 20 SAA and pro-regime militia fighters and wounded others in the ambush on the rescue force near Mount Bishri, between Sukhnah and Deir Ezzor on Thursday.

According to Amaq, the ambushed force had been tracking ISIS fighters in response to the attack near Kom on Wednesday, after which ISIS claimed to have killed 15 pro-regime fighters.

Posts on pro-regime social media accounts appeared to corroborate the attacks, stating that at least a dozen were killed or missing, including an SAA colonel.

Liwa’ al-Quds claimed in the Friday statement its forces had broken the encirclement and killed a number of ISIS fighters. The group published a video purporting to show the engagement.

“We set out from Deir Ezzor, in the direction of al-Haribsha, towards al-Fayda’. After that we arrived at the area of the DD well … where ISIS had besieged the group,” Mohammed Said, the militia’s commander, told al-Mayadeen news channel in a video posted to social media on Monday.

“We were able to break the siege on them [with use of] equipment and fighters,” Said said.

The commander then blamed the U.S. base at al-Tanf for the continued presence of ISIS fighters in the area, a common claim of pro-Assad regime forces.

Liwa’ al-Quds did not claim any casualties during the operation on Friday, and said that its forces were “able to withdraw the bodies of the martyrs, rescue the wounded and withdraw all the disabled vehicles and move all the elements into a safe area.”

A spokesperson for Liwa’ al-Quds did not return requests for comment.

Founded in 2013, the militia has significant Palestinian membership and played a key role in regime operations to recapture Aleppo. The group receives support and training from Russia, according to its Facebook page and an RT report earlier this year.

Syria’s National Defense Forces militia has twice claimed in recent weeks that SAA-affiliated forces have been conducting anti-ISIS clearing operations in the Badia, including near Haribsha.

In an apparently separate incident earlier last week, Liwa’ al-Quds announced the death of 10 of its fighters, including a commander, Imad Zakaria Jammu, south of al-Mayadin during operations to “cleanse” the area of “Daesh gangs.”

Pro-regime forces have been hit with a number of ambushes and improvised explosive device attacks in the desert west of Homs in recent months.

Earlier this month, Amaq released video claiming to show a captured SAA officer and two Russians, who appear unconscious. In the video, a visibly wounded man identifies himself as Munzir al-Assas, a brigadier general in the Syrian Arab Army.

Last month the Syrian Democratic Forces, backed by the U.S.-led Coalition, recaptured the last remaining ISIS territory in Syria, but the group is believed to maintain significant presence in the Badia desert, as well as sleeper cells across Iraq and Syria.

On April 8 ISIS announced its “Vengeance for Sham” campaign, branding a string of attacks across Iraq and Syria as retaliation for the group’s territorial defeat in eastern Syria’s Baghuz.

The U.K.-based Syrian Observatory for Human Rights said on Saturday that “at least” 69 pro-regime fighters have been killed across Syria over the last month, many of them by ISIS ambushes and IEDs in the Badia.