Tuesday's blast at the Khan Research Laboratory (KRL) near Islamabad involved only conventional explosives and not nuclear material, Major General Shaukat Sultan told AFP.

"The technician was handling normal, conventional material," Sultan said. "It was an accident and the cause of the explosion is being looked into."

KRL, founded by A.Q. Khan in the 1970s, played a key role in uranium enrichment leading to Pakistan's nuclear weapon tests in May 1998, which were in reaction to similar detonations by rival India.

Khan admitted in 2004 that he had leaked atomic secrets to Iran, North Korea and Libya. The scientist is being held under house arrest but has been pardoned by President Pervez Musharraf.