Nawabzada Nasrullah Khan, the leader of Pakistan's main opposition grouping -- the Alliance for the Restoration of Democracy -- died in Islamabad of a heart attack late on Friday night.

Media reports described him as Pakistan's greatest democracy advocate.
 
His career spanned half a century and saw him take on several of Pakistan's military dictatorships, his party's spokesman said on Saturday.

Khan was admitted to a hospital in Islamabad on Tuesday after he complained of chest pain during a meeting of senior party leaders.