Fazlullah is the architect of a nearly two-year Taliban campaign to enforce a stricter interpretation of the sharia (Islamic law) in the Swat valley.

He has been on the run since the beginning of the army offensive in late April.

Bounty

Pakistan has offered a $615,000 reward for information leading to Fazlullah's death or capture.

Fazlullah and his supporters are believed to have beheaded opponents, burned schools and fought against  government troops since November 2007.

He is a son-in-law of the pro-Taliban religious leader Sufi Muhammad, who secured a government deal to put three million people in the northwest under the sharia in February.

The agreement later collapsed after Taliban fighters stormed several towns and the government responded by launching the military offensive.

Pakistan's northwestern region has become a stronghold for both al-Qaeda and Taliban fighters who fled Afghanistan following the US-led invasion that toppled the Taliban government in 2001.

Baitullah Mehsud, another Taliban leader who allegedly has ties to al-Qaeda, already has a $5m bounty on his head.

The US state department considers him "a key al-Qaeda facilitator in the tribal areas of South Waziristan".