A suicide bomber attacked police in Pakistan's lawless tribal belt on the Afghan border yesterday, killing 13 people, including seven policemen, officials said.

"The death toll has risen to 13. Seven are khasadar (tribal policemen) and we are trying to ascertain the identity of six others," Shafeerullah Wazir, the administration chief of Khyber, told AFP.

Rehan Gul Khattak, a local official, also gave a death toll of 13.

In Peshawar, a Pakistani military helicopter crashed while in action against militants in the country's northwest tribal belt on the Afghan border on Wednesday, officials said.

The fate of the two people on board was not immediately clear.

The Cobra helicopter was engaged in an operation against militants in the Tirah valley of Khyber, a lawless district that straddles NATO supply lines into Afghanistan, said local administration chief Shafeerullah Wazir.

"It was a Cobra helicopter. It crashed during an operation against suspected militant hideouts in the area," he told AFP by telephone.

A military official confirmed that an attack helicopter crashed, but said the fate of its pilot and copilot was not known.

"We are trying to get details about the cause of the accident and fate of the pilots," military spokesman Major General Athar Abbas said.

Wazirdand is a small town near Pakistan's northwestern city of Peshawar and on the edge of the tribal belt, which lies outside direct government control and has been branded by US officials as the headquarters of al-Qaeda.

Three other vehicles were also damaged by the blast and the shoes and slippers of the victims were scattered across the blood-spattered road, an AFP reporter said.

Rehan Gul Khattak, a local administration official, initially told AFP that six tribal police were killed and authorities were investigating whether it was caused by a suicide bomber or planted explosives.

There was no claim of responsibility, but Taliban and al-Qaeda-linked militants have killed around 3,000 people in bomb attacks across Pakistan, a key US ally in the war in Afghanistan, since July 2007.

Last Friday, at least 33 people were killed in bomb attacks targeting a bus of Shiite Muslim mourners and the hospital where the victims were rushed for treatment in Karachi, Pakistan's biggest city.