SFAX, TUNISIA - More than 200 police officers protested in Tunisia's second city of Sfax on Wednesday to demand the release of eight arrested colleagues and defend their right to unionise, an AFP correspondent said.

Responding to a call from the SNSI police union, the plainclothes protesters chanted pro-union slogans and criticised what they called "harassment" and a drive to stifle union rights.

Eight officers were arrested on Friday after clashes broke out at a sit-in in Sfax, also organised by the SNSI, that sought to press "social and professional demands", union spokesperson Chokri Hamada told AFP.

The SNSI had set up 32 tents in locations across Tunisia and refused to comply with dispersal orders from police deployed by the authorities.

Clashes broke out between unionised officers and the Sfax security forces at Friday's demonstration.

A military court ordered the eight be placed in detention.

They were accused of "harming public security", according to Hamada and local media.