Plain-clothed intelligence operatives "kidnapped" Khalid Khawaja, chief of an organisation called Defence of Human Rights, from outside his Islamabad home early Friday, his family said.

Khawaja's daughter Rabia said on Saturday that police rang the family to inform them he was being held at a police station in the Pakistani capital but gave no reason of his detention.

"This is blatant violation of human rights, first they kidnapped him and now they say he was in the police custody," she told AFP.

Khawaja's organisation has been leading a campaign to find missing people widely believed to be held by secret agencies in the "war on terror".

Pakistan's Supreme Court recently took up the cases of some 41 missing people after petitions by relatives who believed they were being held in the custody of intelligence agencies for undisclosed reasons.

The government later told the court 25 people had been traced and released, but the remaining 16 could not be found.

Police sources said Khawaja, who previously worked for ISI, the Pakistani intelligence agency, was held for organising a demonstration last Friday when thousands of Islamic activists protested against President Pervez Musharraf's approach to the Kashmir dispute.

The country's own Human Rights Commission has said close to 200 people had disappeared in recent years and were believed to be held by intelligence agencies.

Many of them are ethnic nationalists from restive Baluchistan province and also suspects belonging to banned Islamic militant groups.