"The authorities freed activist Abdo Khallaf Wallo, 65, after his health deteriorated," said Qorabi, who heads the National Organisation for Human Rights in Syria.

Qorabi told AFP the detention of the former leader of the Democratic Union party was linked "to his political activity in general and to his role in the events of March 2004".

Opposition political parties are banned in Syria, which is ruled by the Arab nationalist Baath regime of President Bashar al-Assad.

In March 2004, several days of deadly clashes in the town of Qamishli, northeast of Damascus, pitted Kurds against the security forces and Arab tribesmen.

The authorities said 25 people were killed, but Kurdish sources put the death toll as high as 40.

Damascus views the expression of Kurdish language and culture as a threat to national unity and Kurds are frequently arrested for alleged separatism.

The Kurdish population in Syria is estimated at 1.5 million, about nine percent of the population.

Qorabi called for the Syrian authorities to implement an amnesty for the events of March 2004, saying that while Wallo's release was "a step in the right direction", 46 suspects were still facing trial for the unrest.