In the referendum next month, Algerians will be asked to approve a peace plan which includes a wide-ranging amnesty for Islamist militants, and reduced prison terms for those serving sentences.

It was promised by President Bouteflika when he came to power in April.

On the eve of the referendum, suspected Islamist militants carried out the worst single attack on civilians since Mr Bouteflika was elected four months ago.

Twenty-nine people were discovered with their throats cut in a village Beni Ounif in the western Bechar region.

The Algerian security forces have launched a big search.