A judge in Mozambique has found two journalists and an academic guilty of defamation over a Facebook post.

On Monday, a judge found economist Carlos Nuno Castel-Branco guilty of defaming former President Armando Guebuza after he criticized the southern African leader in a 2013 Facebook post.

The judge also found journalists Fernando Mbanze and Fernando Veloso guilty of libel for republishing the commentary. They will be sentenced in September.

A statement from rights group Amnesty International said the trial was a tactic used by the Mozambican government to "stifle dissenting voices."

Mozambique's state news agency said the country's National Union of Journalists demanded the charges be dropped.

The agency reported that the men were tried under a sweeping state security law, which classifies defaming a president as a security offence.