(Updates with reported beheadings)
MINGORA, Pakistan, Oct 26 (Reuters) - Troops battled militants near the stronghold of a Taliban-style movement in northwest Pakistan on Friday, a day after a suicide bomber killed 21 people in the area, 17 of them soldiers, security officials said.
Troops hit back with mortar bombs and gunfire after followers of a pro-Taliban cleric fired rockets at them in the scenic northwestern valley of Swat, where more than 2,000 soldiers have been deployed in response to growing militancy, the officials said.
Residents said they had heard several loud explosions in the Imamdheri area during the hours-long battle, and helicopter gunships were whirring overhead.
"There was some fire exchange between Frontier Corps troops and militants in the area," military spokesman Major General Waheed Arshad told local television. "The army has not suffered any casualties."
Television footage showed a helicopter hovering over a settlement, followed by a loud blast that sent a spray of debris into the air.
Swat has seen a surge in militant activity since Maulana Fazlullah, a pro-Taliban cleric, reportedly launched an illegal FM radio station and urged people to join a jihad or Muslim holy war.
Fazlullah is de facto head of a pro-Taliban group, Tehrik-e-Nifaz-e-Shariat-e-Mohammadi (TNSM) or Movement for the Implementation of Mohammad's Sharia Law, which was banned by U.S. ally President Pervez Musharraf in January 2002.
A spokesman for Fazlullah, Siraj-ud-din, told Reuters one of their comrades had been killed and four wounded in Friday's battle. He said the group had taken two soldiers on foot patrol and two police in the area hostage.
"We fired on security forces when they tried to cross a river into our area," he said. "We had warned them not to cross."
A Fazlullah aide, meanwhile, later said on the group's FM radio channel that the four had been beheaded in the town of Matta, 15 km (nine miles) from the site of the fighting. Witnesses confirmed the beheadings, but did not know the identity of those killed.
The police and the military said none of their men were missing.
Militants have attacked security forces and carried out bomb attacks in recent months in Swat where they have been forcing residents to follow a strict Islamic code.
Siraj-ud-din denied that the group had been involved in Thursday's suicide attack.
Pakistani tribal areas have been a hotbed of support for al Qaeda and Taliban militants who have fled Afghanistan. Thousands of soldiers and militants have died in battles in these regions.
Violence has escalated across Pakistan since July, when militants scrapped a peace deal and the army stormed a radical mosque in the capital, Islamabad.
Officials suspect Islamist militants were behind the worst blast in Pakistan's 60-year history, when at least 139 people were killed in Karachi last week in a suicide attack on a procession led by former prime minister Benazir Bhutto on her return from eight years of self-imposed exile. (With reporting by Augustine Anthony)
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