Mirza Tahir Ahmad, who as Khalifatul Masih IV had been the spiritual leader of the Ahmadiyya Movement since 1982, died April 19 in London after a heart attack. He lived in London.

Mr. Ahmad, who was born in 1928, led an Islamic sect that was noted for its devotion to peace. A 1994 article in The Washington Post about the opening of the Ahmadi American headquarters in Silver Spring told of the group's commitment to missionary work that had brought the sect's numbers to 10 million. It has members in more than 160 countries.

The Ahmadis have been condemned and persecuted by mainstream Muslim groups since the group's founder, Hazrat Mirza Ghulam Ahma, proclaimed himself a prophet of Allah in 1889. Mainstream Muslims maintain that Muhammad was the last messenger of Allah.

Mr. Ahmad was born in Qadian, India, and moved to Pakistan in 1947 following the partition of the subcontinent and the creation of Pakistan and an independent India. In the 1950s, he attended the University of London's School of Oriental and African Studies. He left Pakistan for London in 1984, following the promulgation of anti-Ahmadi laws by the Pakistani government.

Over the years, he visited schools and hospitals organized and operated by the Ahmadis. He also helped supervise Ahmadi publishing operations and helped create international humanitarian aid operations.

Mr. Ahmad was the author of such books as "Murder in the Name of Allah" and "Revelation, Rationality and Truth."