The Syrian Observatory for Human Rights says at least 128 people were killed by IS militants in the Syrian town of Qaryatayn.
The Islamic State militants came into the Syrian town with a hit list. By the time they left three weeks later, more than 100 civilians had been killed - shot or beheaded, their bodies dumped in farms and ditches.
The apparent revenge killings in the town of Qaryatayn underscore the ability of the extremists to inflict heavy losses even when they're in retreat - and portend more violence as they fight to hang on to their last strongholds in Syria.
News of the gruesome slayings began to emerge late Sunday, after IS militants were driven out by advancing government troops.
Terrified residents said they watched the slaughter from their windows or in the streets.
"They came into town with a hit list," said Abdullah AbdulKarim, adding that 35 of the 50 militants who overran the town late last month were originally from Qaryatayn. He said the militants accused many of their victims of collaborating with the government but many others were also caught in the revenge killing.
Once a predominantly Christian town known for its ancient monastery, Qaryatayn has changed hands between IS and the Syrian government several times during Syria's civil war. Parts of the 1500-year-old St Elian monastery were demolished the first time IS took over the town in 2015 and thousands of its Christian residents fled.
An AP video, filmed as Syrian government troops recaptured Qaryatayn on Saturday, showed several bodies lying in the streets. A town resident said IS "monsters" killed more than 100 people, including soldiers and civilians.
"They killed children and women with knives, they beat women, broke their arms," he said.
The Syrian Observatory for Human Rights said it had documented the killings of at least 128 people in Qaryatayn, including at least 12 killed by government forces on suspicion of aiding the IS militants.
AbdulKarim and Mohamed Hassan, an activist who runs the Palmyra Network News, put the death toll at 75 civilians, saying many more remain unaccounted for.