Amnesty International is calling on British lawyers to take “urgent action” on behalf of an Algerian lawyer jailed after a trial which Amnesty said “clearly violated international standards”.

Human rights lawyer Rachid Mesli was sentenced to three years in prison in Algeria this month on charges of having “encouraged terrorism”.

But Amnesty spokeswoman Aminah Magambo claimed the charges against Mesli were changed during the trial. He was originally charged with “belonging to a terrorist organisation”. Mesli denied any link with terrorism and said he was being persecuted for his human rights work.

“He was convicted on a charge which was not brought against him and he was not given the opportunity to defend himself,” said Magambo.

“This is against the International Convention on Civil and Political Rights to which Algeria is signed up.”

She added: “No independent observers were allowed in the courtroom and witnesses for the defence were not called.”

Mesli had earlier disappeared for a week after Algerian security forces arrested him at gunpoint. He claims he was beaten and threatened with death.