PESHAWAR: Pakistani attack helicopters on Monday killed 20 militants and destroyed four hideouts, including a training centre for suicide bombers in the northwest tribal belt, the paramilitary said.

The operation was carried out in Tirah valley, 35 kilometres (21 miles) southwest of Landi Kotal, the main town in the notorious Khyber tribal region that straddles a main supply route for NATO troops in Afghanistan.

"Military helicopters shelled militant hideouts Monday afternoon killing 20 rebels and destroying four of their hideouts," a spokesman for the paramilitary Frontier Corps, Major Fazal-ul-Rehman, told AFP.

He said that the hideouts included a training centre where rebels used to train suicide bombers and Islamist foot soldiers, adding that the air strikes were ordered after an intelligence tip-off.

Death tolls released by Pakistan are impossible to confirm in areas that are remote and largely cut off from independent media coverage.

Hundreds of Islamist fighters are believed to have fled Afghanistan into Pakistan's semi-autonomous tribal areas to carve out safe havens after the US-led invasion toppled the hardline Taliban regime in Kabul in late 2001.

Pakistan has switched attention back to the tribal areas after summer campaign against the Taliban in and around the northwest district of Swat, once dubbed the "Switzerland of Pakistan" for its scenic mountain resorts.

Prime Minister Yousuf Raza Gilani said earlier this month that the military had "eliminated" extremists, although deadly skirmishes have continued in and around the Swat valley, where the Taliban focused on a two-year rebellion.

Pakistan says around 1,800 militants and more than 166 security personnel have been killed in the operations in Swat, neighbouring Buner and Dir.

Fighting forced 1.9 million people to flee homes in the northwest since last year, although the authorities say nearly 400,000 people have returned.