Musharraf is trying to show that he is indispensable, but he is not

Nasrullah Khan, opposition alliance leader

The 15-party Alliance for the Restoration of Democracy said it considered President Musharraf's initiative unconstitutional and would hold peaceful rallies to oppose it.

The alliance includes Pakistan's two main political parties - the People's Party and the Muslim League.

The alliance said it would ask leaders of the two parties and former prime ministers - Benazir Bhutto and Nawaz Sharif to return from exile and strengthen its challenge.

General Musharraf announced on Friday that the vote would be held next month.

Widespread criticism

The plan has already been attacked by Islamist parties and the Human Rights Commission of Pakistan.

Musharraf will launch campaign from Lahore

The hardline Jamaat-e-Islami party has asked the Supreme Court to prevent the referendum from taking place.

The party has filed a constitutional petition against the referendum.

The Commonwealth Secretary-General, Don McKinnon, was the first prominent world leader to criticise the move.

A US state department spokesman suggested that Pakistani courts should decide if the vote is constitutional.

General Musharraf plans to launch his referendum campaign in the eastern city of Lahore on Tuesday.