Two civilians were killed in the fighting that broke out at the village of Imam Dheri, where Fazlullah has a religious school.

A day earlier, a blast hit a security forces vehicle in Swat, killing about 20 people and wounding another 35, after the arrival of more than 2,000 Pakistani soldiers in the area earlier this week.

'Mullah radio'

Badshah Gul Wazir, the interior minister of the NWFP bordering Afghanistan, confirmed that four men had been beheaded.

"I know they were four, and they have been beheaded," he told a news conference in Peshawar, the provincial capital.

There were reports that fighters had abducted a total of eight security officials, but Wazir would not confirm the total number of kidnapped personnel.

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Another policeman said it was unlikely Fazlullah was inside the building.
In an FM radio broadcast on Wednesday, the cleric reportedly announced he was shifting to neighbouring mountainous district, Kohistan.
Fazlullah is known as Mullah Radio for his fiery radio speeches in which he calls for the imposition of Islamic Sharia law and for attacks on Pakistani security forces.
A correspondent of the AFP news agency at the scene said Pakistani troops were firing heavy weapons from hilltops around the cleric's headquarters but were not aiming directly at the compound.
The mullah's supporters were firing at the troops, he said.

Ambulances were on standby to retrieve the injured or dead although there were no details yet on casualties, police said.
Suicide blast probe
Separately, Pakistani security officials investigated the scene of Thursday's deadly suicide bombing.
It remained unclear who orchestrated the attack, which killed one civilian and 19 paramilitary soldiers and left three dozen wounded.
But the assailants appeared to have inside information about the movement of security personnel, Fazlur Rehman, the local mayor, said.
Local men watch the clashes
in the Swat valley [AFP]

The bomber hit a truck carrying about 45 Frontier Constabulary forces near the main police station in Swat.

The Swat valley was once one of Pakistan's premier tourist spots, attracting a large number of foreign guests drawn by its Buddhist heritage and archaeological sites.
But the area has, in the past two years, become a stronghold of Fazlullah's banned group, Tahreek Nifaz-e-Shariat Mohammadi (TNSM).
Security officials say the group is linked to al-Qaeda network and Afghanistan's ousted Taliban.
The worsening situation in Swat is seen by analysts as evidence of the growing "Talibanisation" of previously peaceful areas that border Pakistan's lawless tribal belt along the Afghan frontier.
Pakistan has around 90,000 troops in the tribal belt combating Taliban and al-Qaeda fighters who fled Afghanistan in 2001, as well as their Pakistani supporters.
More than 250 people, including about 50 soldiers, were killed in battles in the tribal region of North Waziristan earlier this month.