Amnesty International has called for a UN-backed investigation into the violence in Syria, saying the regime's crackdown on pro-democracy protesters may constitute crimes against humanity.
The group has documented several cases of torture, deaths in custody and arbitrary detention in a new report.
All relate to a military sweep in the western village of Tell Kalakh in May.
Amnesty says the UN Security Council must refer Syria to the International Criminal Court (ICC) in the Hague.
Syrian human rights groups have said that more than 1,350 civilians and 350 security personnel have been killed across the country since protests began in mid-March against the repressive rule of President Bashar al-Assad, who is fighting off the most serious challenge to his family's four decades in power.
The Syrian government has not responded to the report, but it claims that many of those who have died were the victims not of the army, but of armed criminal gangs.
Syrian state media has also reported on what it said was a large pro-government demonstration in Tell Kalakh late last month.
"The accounts we have heard from witnesses to events in Tell Kalakh paint a deeply disturbing picture of systematic, targeted abuses to crush dissent," said Philip Luther, Amnesty International's Middle East and North Africa Deputy Director.
Witnesses have told Amnesty that Syrian security forces fired on fleeing families on 14 May, the day the army entered Tell Kalakh, near the Lebanese border, following a demonstration in the village calling for the downfall of the regime.
At least one person, 24-year-old Ali al-Basha, was killed, apparently by snipers, and the ambulance carrying his body came under fire, witnesses said by phone and in Lebanon. Amnesty has not been allowed to enter Syria.
In the following days, scores of male residents were rounded up and detained. Most were tortured, Amnesty says, some even as they were being arrested.
In one incident, soldiers transporting detainees counted how many they had arrested by stabbing lit cigarettes on the backs of their necks, Amnesty said in its report, titled Crackdown in Syria: Terror in Tell Kalakh.
The report highlights the case of a 20-year-old, identified only as Mahmoud, who says he was jailed for nearly a month, including five days at a detention centre in Homs, where he was tied up in stress positions and tortured.
"Each day [was] the same story," he told Amnesty researchers. "They tied me up in a shabah position [strung up by the wrists and forced to stand on tiptoes] and applied electricity to my body and testicles. Sometimes I screamed very loudly and begged the interrogator to stop. He didn't care."
Witnesses say at least nine people from Tell Kalakh died while in custody. Their bodies showed signs of torture, including cuts to the chest, slashes on the thighs and apparent gunshot wounds on the legs, Amnesty was told.
The London-based international rights group says that a number of Tell Kalakh residents remain in detention, including a 17-year-old boy. It called on the authorities to free them immediately.
"Amnesty considers that crimes committed in Tell Kalakh amount to crimes against humanity as they appear to be part of a widespread, as well as systematic, attack against the civilian population," Mr Luther said in a press statement that accompanied the report.
The organisation reiterated its call on the UN Security Council to refer the situation in Syria to the ICC prosecutor in the Hague so that legal proceedings could be taken.
The call comes as the Syrian authorities continue their crackdown in the central city of Homs, killing at least nine people in two days and arresting around 500 across the country over the past few weeks, according to Syrian human rights groups.
On Tuesday, France again called for the UN to act against the "ferocious armed repression", but the French campaign for UN condemnation has met resistance from Russia and China.
The Syrian authorities - who blame "armed gangs" and "terrorists" for the unrest - are pushing for a national dialogue next week. But the opposition has refused to participate while the violence continues.