Bashar al-Assad ordered the prisoners' release

Aktham Nueisa, head of the Committee for the Defence of Human Rights, said that two of the released prisoners were senior members of the Muslim Brotherhood who had been behind bars for 15 years, while some of the Baath party members had spent 20 years in jail.

Mr Nueisa said most of the dissidents were detained before Hafez-al-Assad's death in July 2000, after which his son, Bashar Assad, became president.

Syria imprisoned many members of Islamist groups after crushing an uprising by the Muslim Brotherhood in the city of Hama in 1982, in which 25,000 people are believed to have died.

More detainees

Nine prisoners from the Syrian Communist Labour Party were released earlier this week.

But human rights groups say that the Syrian authorities are still detaining 1,200 more political prisoners and prisoners of conscience.

In response to the first wave of releases, Mr Nueisa said there was no indication that Syria would free a separate group of opposition figures arrested in September after calling for greater political freedom.

They include two liberal members of parliament, Maamun Homsi and Riad Seif. The MPs have been on trial since the end of October, charged with trying to change Syria's constitution by illegal means.

If convicted, they face sentences of between five years and life in jail.