Security forces backed by helicopter gunships on Friday attacked a seminary run by radical cleric Maulana Fazlullah, sparking exchanges of fire with militants in a mountainous region of Pakistan's North West Frontier Province.
Officials said there were no reports of casualties while a rebel spokesman said at least four militants had been killed.
The fire fight erupted after militants fired rockets at an army helicopter that was on a surveillance mission with the inspector general of the Frontier Corps, Maj Gen Muhammad Alam Khattak, on board.
There were several explosions and heavy exchanges of fire as the ground forces advanced towards Fazlullah's sprawling seminary at Imamdheri, about three kilometers from Mingora, the headquarters of Swat district.
At least six helicopter gunships took part in the operation, pounding the areas around the seminary. Ground forces from the Frontier Constabulary also used mortars against the militants.
Armed militants inside the seminary fired rockets and exchanged small arms fire with troops who had surrounded the area and taken up positions on nearby mountain peaks. The security forces targeted a building where Fazlullah had been seen in recent days. Later in the day, the exchanges of fire became intermittent.
Many local residents fled the area after the clashes even as troops established more check posts and took over a militant training camp in Khawazkhela tehsil. Many schools and markets in the area were closed.
Maulana Fazlullah, who also heads the outlawed Tehrik Nifaz-e-Shariat Mohammadi that sent hundreds of fighters to Afghanistan, has reportedly left the area and shifted to Kohistan, some 200 km from Mingora.
The clashes came a day after 22 people were killed and over 30 injured when a suicide bomber blew up a truck carrying Frontier Constabulary personnel and ammunition at Mingora.
Among the dead were 18 security personnel and civilians. Military spokesman Maj Gen Waheed Arshad said the army had not launched any operation in the NWFP and was on 'standby.'
He said army helicopters were providing cover to personnel from the Frontier Constabulary and Frontier Corps on the ground.
"The army is on standby and if the provincial government makes a request, then they will also join the operation against the miscreants," he said.
Thousands of troops were deployed in the Swat area earlier this week to counter the activities of Fazlullah, known as 'Mullah Radio' for his calls for jihad broadcast on an illegal FM radio station, and to restore the writ of the local administration in 59 villages where the cleric's armed followers are running a parallel government.
The Tehrik Nifaz-e-Shariat Mohammadi was set up by Fazlullah's father-in-law Sufi Muhammad in 1992 and banned by President Pervez Musharraf in January 2002. Sufi Muhammad was arrested on his return from Afghanistan and has been imprisoned since then.
