|Many rebels in Syria obey no single line of command and do not answer to the political opposition [AFP]
An international human rights group has accused Syrian rebels of kidnapping, torturing and executing members of the security forces, pro-government armed gangs and other government supporters.
Human Rights Watch on Tuesday called on Syrian political opposition leaders to condemn the abuses.
"The Syrian government's brutal tactics cannot justify abuses by armed opposition groups,'' said Sarah Leah Whitson, Middle East director at Human Rights Watch. "Opposition leaders should make it clear to their followers that they must not torture, kidnap, or execute under any circumstances.''
The group said witness statements indicated that some of the attacks were motivated by sentiments against the Shia and Alawite minorities. President Bashar al-Assad and his family are Alawite and have promoted Alawites into top positions in the government and army.
Tuesday's statement comes months into an uprising against Assad, with army defectors and armed civilians carrying out a guerilla war to defend their towns and weaken his power.
The intensity of the fighting has increased since early February, when the government began large-scale military attacks against opposition strongholds throughout the country.
The uprising began a little over a year ago, when peaceful protests inspired by anti-authoritarian movements in Tunisia, Egypt and Yemen broke out. But the regime cracked down violently, opening fire on demonstrations and rounding up thousands of protesters.
Human Rights Watch noted that the rebels reported to be carrying out abuses did not appear to belong to an organised command structure or follow orders from the council, but it called on the Syrian National Council, the largest expatriate opposition group, to speak out and condemn them.
The SNC recently announced the creation of a military liaison office to co-ordinate with the armed groups.
"There are dozens and dozens of armed groups ... and they work compeltely independent of each other," Nadim Houry, the group's deputy Middle East and North Africa director, told Al Jazeera.
"We are calling on [the SNC] to use its moral standing and leadership to condemn these abuses and steer away and say, 'We can oppose the regime in different ways."
Assad has justified the crackdown by saying terrorists and foreign fighters are driving the revolt, and the government has used the increasing attacks on security forces and military sites as vindication that it is facing an extremist threat.
The most potent armed group fighting Assad's security forces is the Free Syrian Army, made up of army defectors and others. But there are other, smaller groups operating as well.
The report cited witnesses who told Human Rights Watch that armed groups identifying themselves with the opposition were kidnapping both civilians and members of the security forces.
It also cited several YouTube videos and statements by rebel fighters that indicated pro-government militia known as shabiha and intelligence officers had been executed.
In-depth coverage of escalating violence across Syria
An activist identified as Mazen said he learned that three people who worked with the government had been tortured to death in Idlib in northern Syria, an opposition stronghold. He said another member of the Syrian security forces who had been kidnapped was allowed to call his parents so that he could be ransomed.
Another Syrian activist identified as Samih told HRW that residents of the town of Saraqeb complained to the FSA on more than one occasion that the al-Nur battalion, a Salafist group that is not part of the official FSA structure, was kidnapping civilians for ransom. Samih also said the FSA were kidnapping soldiers for ransom.
"They would kidnap them and ask their parents to pay a ransom to let them go,'' Samih said, according to Human Rights Watch.
The Free Syrian Army denied kidnapping soldiers, saying they were detaining them during military operations.
The United Nations says more than 8,000 people have been killed in the year-long uprising, which has deeply polarised a country where the Assad family has ruled for more than 40 years.