Hundreds of Pakistanis rallied against an army operation in the North Waziristan tribal area which they say killed many civilians.

About 300 people, mostly students from North Waziristan, took to the streets in the frontier city of Peshawar to denounce the operation and demand an investigation.

Student Zahidullah Khan said his aunt had been killed by military shelling.

"The army is claiming they have killed militants and terrorists. They think my aunt was a terrorist?" he said.

The army said the operation began when a military convoy came under attack in the tribal area late on Wednesday.

The convoy had rushed to the aid of soldiers wounded and killed in a suicide bomb attack on a checkpoint outside an army base.

Its soldiers killed at least 23 militants when they returned fire, then 10 more militants the next day, according to the military.

The army said most of those killed were believed to be Uzbeks. North Waziristan is home to many militant groups including foreign fighters who use the area as a base for attacking Nato troops in Afghanistan.

But residents accused the military of killing innocent civilians. Akhtar Khan and Arif Dawar, from Mir Ali where the clashes happened, said many of the dead were civilians.

In the bazaar area of Mir Ali, local resident Aershad Khan said most of the shops had been burned and damaged by government shelling.

He said residents were searching damaged buildings and gutted shops for bodies and wounded.

"The fruit market is totally gutted with fire and nothing is left there but ashes," Khan said.

North Waziristan is one of Pakistan's most dangerous and remote areas, making it difficult to verify the army's claims.

Residents of the tribal areas often accuse the military of indiscriminately opening fire after they are attacked.

The military disputes that and says militants often dress in civilian clothes to hide among the local population.

The vast majority of US drone strikes in Pakistan have targeted North Waziristan.