By Stephanie Irvine BBC North Africa Correspondent

The Appeal Court in Tunis has started hearing an appeal against prison terms imposed on a prominent opposition figure, Hamma Hammami, and two colleagues.

The men have been sentenced to over nine years for being members of the outlawed Tunisian Communist Workers Party.

The last time the men appeared in court, in February, they were dragged away by police and imprisoned without getting a hearing.

A heavy police presence outside the court allowed access only to accredited journalists and observers, including several from foreign human rights groups which have called for the defendants' unconditional release.

Picture of Hamma Hammami, courtesy of Amnesty International

The men - Hamma Hammami, Abdeljaber Madouri and Samir Ta'amallah - were convicted in absentia of dissident activity three years ago, when they were in hiding.

They gave themselves up on 2 February this year to challenge their convictions but their retrial soon descended into chaos.

Witnesses said the men were dragged away by police, to re-emerge later with torn clothes and complaining of having been beaten.

The judge then upheld their convictions and the men were taken to prison.

Mr Hammami went on a week-long hunger strike, which he ended on Tuesday, in protest against the conditions in which he was being detained.

'Common criminal'

His lawyer and wife, Radia Nasraoui, says he is being held with dangerous criminals and that access by legal counsel and family has been severely restricted.

The Tunisian authorities say Mr Hammami is a common criminal and has been convicted for breaking the law, not for his opinions.

This case has come up as Tunisia's President Ben Ali faces strong international criticism of his government's handling of opposition parties and human rights issues.

Human rights groups accuse the Tunisian authorities of using the courts to silence political opponents.