Peshawar - At least nine army troops were killed on Monday in a suicide attack in north-west Pakistan, officials said.

Army spokesman Major Murad Khan told Deutsche Presse-Agentur dpa that a bomber rammed an explosives-laden vehicle into security forces' headquarters located in Madyan area of restive Swat valley in North West Frontier Province.

"Three soldiers were martyred at the spot while six succumbed to their injuries in the hospital," he said.

Earlier, thousands of people protested the killing of three civilians allegedly by army shelling.

The demonstration started after a mortar round hit a house in the Allah Abad area of Swat district, leaving a women and her two children dead, local journalist Nisar Ali Khan said.

Residents transported the victims' bodies to the Mangora city, where the army headquarters is located, some 20 kilometres away. More than 8,000 people joined them, while thousands gathered on the streets to express solidarity with the protestors.

As the rally arrived in Mangora, security forces used teargas to disperse the gathering but angry demonstrators reacted by pelting state-buildings in the city with stones. Several were injured in the hours-long clashes.

Swat, a once popular tourist destination, has seen intensive fighting between government forces and Taliban militants since last October when Islamabad dispatched thousands of troops to quell the rebellion of the followers of radical cleric Maulana Fazlullah.

Fazlullah had launched an armed campaign to enforce Taliban rule in the area. The new government in Islamabad launched peace talks with militants immediately after it took over in March, but resumed their offensive a month later when the negotiations failed to bring peace to the region.