At least 35 militants were killed in clashes which followed a major attack by the security forces in northwest Pakistan's Orazkai tribal agency on Monday, army sources said.

Two Pakistani security personnel were also killed and another seven troops were injured in the ongoing operation at Shereen Darra area of Lower Orakzai Agency, local officials said.

Officials claimed on Sunday that several bunkers in Orazkai built by militants had been destroyed on Saturday night.

They said the forces had set up their main base camp in Shereen Darra which was vital for the security of Kalaya, a main town in Orazkai.

Militants launched rocket and mortar attacks in Shereen Darra.

Sources said that security forces used helicopters and heavy artillery in the operation and destroyed many of the militants' hideouts.

The army said troops have secured important heights in the area and have also seized arms and ammunition. It said troops have taken control of most areas of the agency and were advancing towards Upper Orakzai Agency.

Security forces backed by helicopter gunships killed over 300 Taliban militants so far in Orakzai since late March when the army launched a fresh offensive in the agency to flush out Taliban.

A statement issued by the army's Inter Services Public Relations in Peshawar said that militants had started fleeing to Tirah valley of the adjacent Khyber tribal region and other parts of the tribal belt and Afghanistan due to the successful operation in Orakzai.

The statement said Tirah, a stronghold of the proscribed Lashkar-i-Islam, had become a hub of Tahrek-e-Taliban Pakistan, Swat Taliban and foreign militants.

It said that militants had established hideouts and training centers in different parts of Tirah.

Pakistani security forces have stepped up assaults in the restive northwest over the past year, largely clearing militants from the tribal areas along the Afghan border.