The Syrian government has released hundreds of detainees, including some who backed the insurgency against President Bashar al-Assad, on the eve of a major Muslim holiday.

Key points: Syria's government releases 672 prisoners who promised to accept its authority

Syria's government releases 672 prisoners who promised to accept its authority Around 200 Islamic State militants said to be preachers or non-combatants are pardoned

Around 200 Islamic State militants said to be preachers or non-combatants are pardoned The prisoner amnesties, common during festive times, come at the end of Ramadan

In northern Syria, the US-backed Syrian Democratic Forces released around 200 IS members in Raqqa province at the request of tribal leaders in the region.

The government said it released 672 prisoners who had promised to accept the state's authority, a move it said was aimed at bolstering a "reconciliation" process.

The process involves rebels either disarming and accepting government rule or leaving with small arms for other insurgent areas.

"They have been released after promising not to do anything against the nation's security or stability," Justice Minister Hisham al-Shaar was quoted as saying by the official SANA news agency.

The opposition, Western countries and rights groups say the government has detained tens of thousands of Syrians without trial for political reasons, torturing and killing thousands of them.

The al-Assad government denies that.

SANA did not report what the freed detainees had been put in prison for, but some of those released said they were arrested for actions they took against the government.

Prisoners in Damascus ahead of their release by the Syrian government. ( Reuters: SANA )

The release came on the eve of Eid al-Fitr, the feast that marks the end of the Muslim holy month of Ramadan.

Among those released in Damascus was 45-year-old Abdul-al-Rahman Ali who used to finance opposition fighters.

"I was wrong and every person makes mistakes. I have repented and returned to embrace my homeland," he said.

A woman who identified herself as Um Akram wiped away her tears as she waited for her son who had been jailed for more than three years.

"I am glad for the release of my son," she said as she stood with her husband outside the headquarters of al-Assad's ruling Baath party in Damascus where part of the release occurred.

The woman's husband stressed that his son is ready to join the military service.

Ibrahim Barakeh, 64, from al-Ghouta in the countryside of Damascus, said he has been in jail for 16 months on a charge of funding terrorists.

"Thank God for being released. I was wrong. I will try to return to al-Ghouta to join my wife and son," he said.

Of those released by the government, 91 of the prisoners were women.

One said she hoped other women would be freed soon.

"I have been detained for a year, it was due to a report which was wrong," the woman said.

"There are still large number of prisoners and we hope another amnesty will emerge and they will be out because they are innocent."

The British-based Syrian Observatory for Human Rights said the Islamic State militants pardoned by the Kurdish-led Syrian Democratic Forces in the northern town of Tabqa and the city of Raqqa had "no blood on their hands".

The monitor said they had jobs with IS such as preachers or employees in the extremist group's civilian institutions.

Reuters/AP