Taliban chief Mullah Mohammad Omar has added to the mystery over Osama bin Laden, saying he had not seen his ally and fellow fugitive since US-backed forces ousted the Taliban from Afghanistan in late 2001.

"No, I have neither seen him, nor have I made any effort to do so, but I pray for his health and safety," Mullah Omar said in an e-mailed response to questions sent by Reuters.

The questions were relayed to Mullah Omar through his spokesman Mohammad Hanif, and a reply was received late on Wednesday. A half-dozen audio tapes of bin Laden were circulated during the first half of 2006, but the al Qaeda leader last appeared on video tape in late 2004, while tapes of his deputy, Ayman al-Zawahri, have been issued regularly.

A video tape of bin Laden was released late last year, but it was identified as old footage, and the fifth anniversary of the September 11, 2001 attacks on the United States passed without any word from the al Qaeda leader.

Speculation over the whereabouts and health of bin Laden boiled over in September when a French provincial newspaper reported that he had died of typhoid in late August.

Several governments and intelligence agencies rebutted that report, saying they had no evidence to suggest bin Laden had died, nor did they have any clue to where he was.

The wealthy Saudi-born bin Laden helped bankroll the Taliban after moving to Afghanistan in the mid-1990s, and he reportedly married one of Mullah Omar's daughters to cement their alliance.

The best guess to bin Laden's whereabouts remains somewhere on the rugged border between Pakistan and Afghanistan, in the ethnic tribal lands where Mullah Omar's Taliban counts on support to fight an insurgency against US and Nato forces in Afghanistan and the government of President Hamid Karzai.