KHAR: Clashes killed six security personnel in the latest setback for Pakistan's fight against Islamists in the tribal belt, where air raids left more than 20 militants dead, officials said Friday.

Some 20 to 25 armed rebels targeted a checkpoint manned by local tribal police overnight near Khar, the main town in the semi-autonomous region of Bajaur, where Islamist militants have a significant presence, officials said.

"The armed militants attacked the post killing all (four) policemen inside," local government official Adialat Khan told AFP.

He said the post, set up to conduct security checks on the main road heading into Khar, was destroyed.

Other security officials confirmed the incident, which came after another government official said gunmen abducted a policeman in Mamoun, 15 kilometres (nine miles) northeast of Khar.

Pakistani security forces launched a huge operation against Islamist militants in Bajaur last August. In February, they claimed the area had been cleared after months of fierce fighting, but unrest has rumbled on.

Hundreds of extremists 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.

On Friday, militants ambushed security forces conducting search operations in the Chinnar and Manoogi areas of Bajaur. Ensuing clashes killed two security personnel and wounded five others, military and government officials said.

Helicopter gunships and artillery were used in the counter-attack in which 12 militants died, local government official Mohammad Jamil Khan told AFP.

Although official Pakistani death tolls are impossible to confirm from such remote areas where there is little or no media access on the ground, the casualty statistics were corroborated by a security and a military official.

In the tribal district of Orakzai, south of Pakistan's main northwestern city Peshawar, more than 10 militants were killed in air raids late Thursday, military and government officials said.

"Militant compounds and hideouts were targeted in the attacks. More than 10 militants were killed in the bombing," a military official told AFP.

It was the second bout of Pakistani air strikes in Orakzai following the deaths of at least 26 security personnel in a helicopter crash in the area.

The military blamed the July 3 incident on a technical fault, but the Taliban claimed it shot down the MI-17 as revenge for military operations in South Waziristan, the heartland of Pakistani Taliban warlord Baitullah Mehsud.

Pakistan, which is under strong US pressure to clamp down on Islamist militants, has pounded suspected Mehsud strongholds in South Waziristan from the air for weeks, ahead of a widely expected ground offensive.