Islamist militants burned down a hotel at Pakistan's only ski resort on Thursday as security in a northwestern tourist valley deteriorated despite a month-old peace pact, police said.

The Swat valley, several hours drive on mountain roads from the capital, Islamabad, was until last year a prime tourist destination with ancient Buddhist ruins, a golf course, trout streams and the ski resort.

"Half of the hotel has been burned down," said Swat's police chief, Waqif Khan, referring to the only hotel at the Malam Jabba ski resort. The hotel is owned by the state tourism authority.

Khan said authorities had not been able to get to the resort to tackle the blaze or inspect the damage.

"The area is not under our control, it's under the militants' control and no one can go there," he said.

Militants infiltrated the valley from the Afghan border last year to support a radical cleric based there. The army began battling the militants in November after the militants resorted to violence in their campaign to impose Taliban-style rule.

The hotel shut down last August as tension in the valley increased. It later dismissed its staff as visitors stopped coming.

The militants and the government of North West Frontier Province signed a peace pact last month but hopes stability would return have been dashed with a surge of violence this week.

Militants have attacked security posts, and police and army patrols and they blew up several girls' schools. Fifteen people have been killed in recent days.

But a militant spokesman denied setting the hotel on fire.

"Our target is the security forces, we have nothing to do with the hotel," said the spokesman, Muslim Khan.

Khan said villagers in the area had appealed to his men to help them stop businessmen he referred to as "timber mafia" cutting trees on the mountain slopes.

"There's a third element which does not want the peace accord to succeed, they don't want peace in the area," he said, apparently referring to the log poachers.