Dozens of people staged a sit-in on a highway in northwestern Pakistan on Wednesday after the army accidentally hit a house with an artillery shell, killing six people, while it was attacking suspected militant hide-outs.

The dead included three women, two children and a man, said a local police official, speaking on condition of anonymity because he was not authorized to talk to the media. The accident occurred in Shahukhel, a town in the Hangu district of North West Frontier Province, he said.

The protesters placed the bodies of the victims on the main highway that runs through the province, blocking traffic, said Hashim Khan, a local resident who attended the demonstration.

The participants chanted "stop the killing of innocent people" and "stop this cruelty," said Khan. The protest lasted about two hours and then dispersed peacefully, he said.

Hangu is close to two areas in Pakistan's semiautonomous tribal region where jet fighters also pounded militant hide-outs Wednesday killing 18 suspected fighters, said intelligence and political officials.

The attacks come as the Pakistani army is waging a major offensive in the South Waziristan tribal area near the Afghan border, where al-Qaida and Taliban leaders are believed to be hiding.

Officials believe many militants have fled South Waziristan, seeking refuge in other parts of the tribal region and elsewhere in Pakistan.

Jet fighters pounded two hide-outs used by militants loyal to Pakistani Taliban leader Hakimullah Mehsud in the Orakzai tribal area, killing 13 suspected fighters, said the officials.

Planes also attacked compounds in the Kurram tribal area, killing five militants who had fled South Waziristan, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

Pakistan's army has pitted some 30,000 troops against up to 8,000 militants in South Waziristan, including many Uzbeks and other foreign insurgents who have long taken refuge in the lawless tribal areas.

Commanders say Pakistani troops have retaken most population centers, roads and strategic high ground in the region but that insurgents remain in parts of the countryside.

The most recent fighting in South Waziristan killed six militants and injured eight soldiers, the army said in a statement Wednesday.

The information is impossible to verify independently since Pakistan has blocked access to the battle zone.