The Syrian Observatory for the Defence of Human Rights said intelligence services picked up Sheikh Murad Khaznawi on Monday near the Jordanian border as he was preparing to leave the country.

It called for his immediate release.

A brother, Murshed Khaznawi, who provided the information, told the London-based group that he feared for his life and accused "influential figures in the Syrian regime" of having assassinated their father in 2005.

The Kurdish Muslim clergy had "received threats from the security services after an April 2005 speech in which he blamed them for the murders of dozens of Syrian Kurds in March 2004", the brother said.

Five days of clashes in March 2004 pitting Kurds against security forces and Arab tribal elements in Qamishli and Aleppo resulted in 40 deaths, according to Kurdish sources. The authorities said 25 people were killed.

Kurds make up around nine percent of Syria's population and charge they are the victims of discrimination in the Arab state.