A Syrian appeal court has upheld 30-month jail terms slapped on 12 opposition figures who called for democratic reforms, a human rights group said on Tuesday.

"The appeal court rejected the motion submitted by defence lawyers for the opposition figures who signed the 'Damascus Declaration'," said the London-based Syrian Observatory for Human Rights.

"We believe the verdict is political and was issued on the basis of inquiries made by the intelligence services to silence all (democratic) voices," the Observatory said in a statement, urging their immediate release.

Abdel-Karim Rihawi, president of the Syrian League for the Defence of Human Rights, reacted by calling for a general amnesty for all political detainees and prisoners of conscience in Syria.

In late October, the 12 signatories of the Damascus Declaration which calls for democratic change were condemned in a court in the Syrian capital for "damaging the state," after a trial of less than three months.

Author Ali Abdullah, Dr Walid Bunni, writer Akram Bunni, and former MP Riad Seif were convicted, as were Fidaa Hurani, Ahmad Tomeh, Jabr al-Shufi, Yasser al-Iti, Mohammed Haji Darwish, Marwan al-Ish, Fayez Sara and Talal Abu-Dan.

Akram Bunni is a brother of human rights lawyer Anwar Bunni, who is serving a five-year jail term.