Syria has released more than 500 prisoners detained in anti-government protests while an opposition group accused the regime of torturing to death 617 jailed people since the uprisings began in March.

Syrian state television said Thursday that those released did not take part in what it called the killing of Syrians, a reference to the protest movement against the government of Syrian President Bashar al-Assad.

But the London-based activist group Avaaz issued a report accusing Mr. Assad's government of widespread murder. The report said scores were killed in overcrowded jails and illegal detention centers.

The group says nearly 7,000 people have been killed in the uprising, while the United Nations has estimated the death toll at 5,000.

Avaaz said it verified the deaths through independent sources, including family members of those killed. The group encouraged Arab League monitors in Syria to visit prisons to pressure the Syrian regime to end the killings.

Earlier this week, Arab League Secretary General Nabil El Araby said the Arab League mission in Syria has secured the released of about 3,500 prisoners.

But the head of the British-based Syrian Observatory for Human Rights said his contacts have not seen the release of detainees.

Arab League observers are in their second week of measuring Syria's pledge to curtail the crackdown against protesters.

Syria's opposition has sharply criticized the observer mission, saying it allows President Assad to continue cracking down on the rebellion against his 11-year autocratic rule.

On Thursday, Qatar's prime minister said the Arab League mission in Syria has made some mistakes. The comments of Prime Minister Hamad bin Jassim al-Thani, who heads an Arab League task force on Syria, came after talks Wednesday with U.N. Secretary General Ban Ki-moon.

Arab League ministers are due to meet Saturday to review the observer team's work.

Syria says it is fighting militants directed from abroad that have killed at least 2,000 of Mr. Assad's forces during the uprising.