PESHAWAR: Clashes between security forces and militants have left 20 people dead in northwest Pakistan over the past 24 hours, officials said Monday, in the latest violence in the troubled region.

The deadliest fighting took place in the northern Swat Valley, where the army is wrapping up an offensive against Taliban militants. The military said in a statement it killed 12 suspected insurgents in a gunbattle near the town of Dardial, while one officer died. Two more militants were killed in the village of Ghul Shah.

The violence shows that security remains fragile in Swat, even as thousands of about 2 million refugees uprooted by the military campaign there began returning home amid a government repatriation program.

Elsewhere in the northwest, insurgents ambushed police on the outskirts of Peshawar, killing four policemen, senior police official Nisar Khan said. The police were patrolling on a road that leads to the Khyber tribal region, an area that has witnessed numerous militant attacks because of its status as a supply route for U.S. and NATO forces in Afghanistan.

In the nearby Bannu area, meanwhile, a roadside bomb killed one Frontier Constabulary officer and wounded seven more, local hospital official Mohammad Jawed said.

No group immediately claimed responsibility the attacks, but Taliban militants in the region frequently target security forces.

Pakistan's military is pursuing its offensive in Swat as it also readies a similar campaign in the South Waziristan tribal region targeting the Pakistani Taliban chief, Baitullah Mehsud.

The U.S. supports the operations, saying Islamabad must eliminate militant safe havens for its own stability's sake as well as to lessen the threat those fighters pose to the U.S.-led war in neighboring Afghanistan.

The Swat campaign has driven some 2 million people from their homes, according to the United Nations. Thousands of the displaced have started returning home now that the military declared the region largely cleared of militants.

EU foreign policy chief Javier Solana, who was in Islamabad Monday for meetings with senior Pakistani officials and visited a refugee camp north of the capital, praised Pakistan's response to the humanitarian crisis.

"I am very, very impressed with the manner in which this complicated operation has been handled," Solana told reporters.