More than 300 people, mostly civilians, were killed in the eastern Syrian province of Deir Ezzor in July, when army operations intensified, the Syrian Observatory for Human Rights said on Tuesday.
Activists recently posted videos showing gory images of bloody, mangled bodies, including women and children, and mutilated faces strewn across several city streets.
In one such video, published on Saturday on YouTube, the trunk of one victim, whose body had been blown off from the waist down, lay across another lifeless man.
The cameraman filmed other bodies and charred skeletons of cars, stopping short at the sound of sniper fire, which he says targets anything that moves.
"Seventeen people have been killed in Deir Ezzor," he says, naming the victims one by one, pausing halfway as gunshots interrupt.
In video posted on Sunday, remains of children lie on the ground with faces blown in, entire limbs missing or halves of their bodies torn away. Others are charred beyond recognition.
"Here is what happened to the women and children of Deir Ezzor (...) we still cannot retrieve their bodies because of shelling and sniper fire," the cameraman exclaims.
The victims, most of them killed by regime gunfire and shelling, had to be buried in back yards and public parks, the Britain-based Observatory said.
The watchdog, which relies on a network of activists in Syria, reported that 70 percent of Deir Ezzor residents have fled the city and that the rest lack the resources to relocate.
It estimated that 500,000 of the 1.6 million inhabitants of the entire province have left for other regions of the country, as shelling dragged on for over a month.
Aside from the humanitarian cost, the devastation caused to the city amounts to 11 billion Syrian pounds ($169 million/137 million euros), according to the watchdog.