His death, if confirmed, would be the second significant terrorist target claimed in a month, after the al-Qaeda leader, Osama bin Laden, was assassinated on May 1.

The two were associates. Mullah Omar, the head of the Taliban regime that controlled Afghanistan between 1996 and 2001, reportedly sheltered bin Laden before and after the terrorist attacks on September 11, 2001.

But there are conflicting reports as to whether Mullah Omar is actually dead.

The Afghan news channel TOLO Television said Omar had been killed as he travelled in Balochistan in Pakistan's lawless border region.

"Mullah Omar was killed on the way from Quetta to North Waziristan," TOLO reported.

The station offered no details on how he was killed or by whom and the claim was quickly rejected as baseless by several Afghan Taliban spokesmen.

"This is pure propaganda. This is not possible at all," one spokesman, Zabihullah Mujahid, said by telephone from an undisclosed location.

Other sources said Mullah Omar was in Afghanistan "safe and sound".

Hamid Gul, the former head of Pakistan's notorious Inter-Services Intelligence agency and a man reported to be linked to Omar's death, said the reports were politically motivated and for a US audience.

"No more Omar, no more Osama, vote for Obama," he told Indian TV.

But rumours of Omar's demise, either by an American drone attack or by the ISI, persisted yesterday. An Iranian news report said a post-mortem examination was being conducted. Several reports said Omar had been missing for 11 days.

Tall and thin, 52-year-old Omar is famously reclusive, and rarely travels.

The few photographs of him show him missing his right eye which was lost to a shrapnel wound during fighting against Soviet troops in the 1980s.

He was head of the Supreme Council of the Taliban regime whose oppressive rule of Afghanistan was ended in 2001 by US forces for supporting bin Laden and al-Qaeda.

In the aftermath of bin Laden's killing by US Navy SEALs in the Pakistani city of Abbottabad on May 1, senior officers in the US military said Omar was a new focus.

"If I was Mullah Omar I would certainly be worried. It shows the Americans are focused," Major-General Richard Mills, a former marine commander in southern Afghanistan, said.

Elsewhere in Pakistan yesterday, vengeance for the killing of bin Laden reached a new peak, with up to 20 gunmen laying siege to a naval base in the country's biggest city, Karachi.

The insurgents, armed with automatic weapons, rocket launchers and hand grenades, stormed the Mehran Naval Station late on Sunday.

In more than 12 hours of fighting, 11 military personnel were reported killed while more than a dozen were injured. It is not known how many militants were killed.

Two US-made P3C Orion aircraft, used for reconnaissance, were destroyed by the gunmen before the insurgents were brought under control.

It is the third insurgent attack against military and diplomatic targets that the Pakistani Taliban have claimed is retaliation for bin Laden's death.