Up to 30 people have been killed and more than 50 injured after a suicide bomber attacked a funeral in North Western Pakistan.

The bomber blew himself up among mourners attending the funeral for one of three policemen killed earlier when their van struck a roadside bomb in the northwestern town of Lakki Marwat, police and medical workers said.

Authorities also made an emergency appeal for blood donations to assist those injured in the attack in the Swat Valley region.

Syed Kamal Shah, North West Frontier Province health minister, told AFP news agency: "We are facing difficulty in the relief operation because the blast also damaged an electricity transformer in the area."

Major General Nasser Janjua, a regional commanding officer, said earlier in the week that 400 fighters were hiding in the valley.

Major offensive

Troops have been searching for Maulana Fazlullah, a religious leader who called for Islamic law in the valley. The army launched a major offensive in November to drive his followers out of Swat.

The mountainous, snow-capped Swat region is renowned for its ancient Buddhist relics and once attracted large numbers of foreign and local tourists, but has since been beset by violence.

Hundreds of people have died across northwest Pakistan in recent months.

A suicide bomb campaign targeting security forces intensified after the army stormed Islamabad's Red Mosque last July.

Last year, about 2,000 people were killed in violence across Pakistan.

PHOTO CAPTION

Pakistani policemen stand next to the wreckage of vehicle after a roadside bomb blast in Lakki Marwat, a town bordering the North Waziristan tribal district.

Al-Jazeera