The bodies of 17 men arrested by Syrian President Bashar al-Assad's forces during an armoured assault this week on the city of Hama were found dumped in the streets after being shot in the head, activists said on Saturday.
The reported killings mark an escalation in a five-month military crackdown on Hama, 240 km (150 miles) north of Damascus, where armed rebels are now backing protesters after tanks stormed the conservative Sunni Muslim city in August.
"They were killed execution style, mostly with one bullet to the head. Iron chains that had tied them were left on their legs as a message to the people to stop resisting," Abu al-Walid, an activist in the city, told Reuters by telephone.
Another activist said the bodies, their hands tied by plastic wire and some with their legs chained, were dumped in the streets of five Hama neighbourhoods on Thursday evening.
"They are of mixed ages. One was in his 60s, another in his 40s and several were in their 20s," he said, adding that only three had been identified, one of whom was a police deserter.
"They (Assad's forces) seem to have dumped the bodies of people from one neighbourhood in a completely different one, making it difficult to know who they are," he said.
Asked whether the bodies could be those of Assad loyalists killed by rebels, the activist said this was not possible.
"Hama is a military zone full of armoured vehicles and troops," he said. "Roadblocks and tanks have isolated districts from each other. The streets are empty and no one dares to drive a car unless he wants to be shot, let alone to move between different neighbourhoods and dump bodies."
There was no comment from the Syrian authorities, who tightly restrict independent media access to the country.
A YouTube video, which could not be independently verified, showed six bodies of mostly young men in a street described as being in the Bab Qabli district of Hama. Their hands were tied and their legs were chained. They appeared to have died from gunshot wounds to the head or neck.
Other bodies were found in the Basateen, Hamidiya, Arbaeen and Masbah neighbourhoods, activists said.
Hundreds of people have been detained, mostly from the anti-Assad strongholds of Bab Qabli and Hamidiya, on opposite sides of the Orontes river, since security forces launched an offensive against Hama, a city of 600,000, on Wednesday.
"Families who fled Hamidiya to other parts of the city last night report seeing bodies on the streets. We don't have the names but at least 15 people were killed from bombardment on Hamidiya yesterday," one resident of the district said.
He said he had been hit by shrapnel in his shoulder and back from a mortar round that struck his house, adding that elite Republican Guard units were spearheading the offensive.
It was the third major attack on Hama since August, when tanks entered the city, scene of some of the biggest protests against Assad since a popular uprising began in March.
At least 30 people have been killed there in the past three days by mortar and heavy machinegun fire as security forces try to dislodge insurgents from parts of the city, activists said.
In 1982, Assad's father, President Hafez al-Assad, crushed an armed uprising by the Muslim Brotherhood in Hama, killing many thousands of people and razing the old part of the city.