"At this point, we have reports of over 20 dead and scores of wounded," the official, who requested not to be identified, told Reuters.

"We are trying to get information. Intial reports suggest it was suicide attack," Interior Ministry spokesman Javed Iqbal Cheema said.

The blast took place when tribesmen were holding a jirga, or traditional meeting, to discuss the security situation in the tribal region of Dera Adamkhel.

Another official said an emergency had been declared at hospitals in neighbouring towns

Over 450 people have been killed in militant related violence this year alone. A suicide bomb campaign targetting security forces intensified after the army stormed Islamabad's Red Mosque last July to crush a militant student movement.

A suicide attack on a police funeral in northwest Pakistan killed at least 38 people on Friday, while on Monday, the army's top medical officer was killed in a bomb attack in Rawalpindi.