PESHAWAR: Deadly skirmishes in Pakistan's Swat valley triggered fresh concern Wednesday about worsening security as the government returned thousands of civilians displaced by a military offensive.

Pakistan said 13 militants and one soldier were killed in Swat in 24 hours despite an announcement that the extremists had been defeated, and many of the 1.9 million people displaced by fighting against the Taliban are worried.

"I fear the security situation may deteriorate in Swat any time," Gul Ahmad Khan told AFP from Barikot, two days after returning home to southern Swat in a government-organised convoy.

Khan, a cook by profession, said he was delighted to leave a crowded refugee camp on scorching low-lying plains, but did not rule out that Taliban fighters could return to a district once dubbed the Switzerland of Pakistan.

The military said 13 militants, including an alleged "terrorist leader" not previously known, were killed during exchanges of fire in Swat, where Taliban fighters waged a brutal two-year campaign to enforce sharia law.

The deadliest clashes were reported near the old militant stronghold of Kabal in the north where the military said eight militants, including two foreigners, and a soldier were killed in a gunbattle.

The alleged militant leader was killed in Peochar, another bastion in Swat -- once believed to have been a headquarters of the local Taliban leadership and where airborne troops saw some of the deadliest fighting this summer.

"It will take so long to bring the situation back to normal," said Nisar Alam, who owns a grocery store in Landakai, elsewhere in southern Swat.

The government has said soldiers will remain in the area and every effort will be made to protect civilians as they try to rebuild their lives.

Wednesday was the second consecutive day on which the military reported killings in Swat after announcing nine deaths on Tuesday following a lull.

"My children are also very scared of army helicopters and start crying when they see them hovering around," said Alam, who returned home this week.

Last week, Prime Minister Yousuf Raza Gilani said the military had "eliminated" the extremists.

The army launched a massive offensive under heavy US pressure in late April in Buner and Lower Dir, before focusing the fight on militants in Swat.

But a senior local police official was sceptical about a quick return to peace in the valley, where gunmen led by cleric Maulana Fazlullah for two years killed, kidnapped, intimidated civilians and fought with the security forces.

"The situation in Swat has not improved to the extent of preventing violent incidents in the valley in the near future," said Sajid Mohmand, the head of police in the valley.

"There are reports that some militants are still hiding in the mountains and these are the elements which may deteriorate the situation in Swat," he said.

Pakistan says more than 1,700 militants and around 160 security personnel were killed in operations to crush the Taliban in northwest districts since late April, but the death tolls are impossible to verify independently.

The government says it has worked hard to restore electricity and running water in main towns since the fighting but analysts warn that much needs to be done to sustain the returnees particularly with Taliban leaders still at large.

Officials said about 2,300 displaced families have so far returned to Swat and Buner since the government-organised returns process began Monday.

"A total of 1,534 families returned to Swat while 757 families headed back to Buner since the repatriation of displaced persons started," a spokesman for the government aid effort, Lieutenant Colonel Waseem Shahid, told AFP.

Azam Khan, a government emergency relief official, said it was difficult to calculate the precise number of returnees, but added that eight to 10 people make up most displaced families.