The convoy was heading to Miranshah, the main town of the North Waziristan tribal district, when the bomber attacked it at around 11:30 am (0630 GMT), top military spokesman Major General Waheed Arshad told AFP.

"The number of soldiers martyred in the attack has risen to 18," Arshad said, updating earlier reports. "Twenty-eight soldiers were wounded.

"More bodies were recovered from the badly mangled wreckage of the vehicles which were hit in the suicide attack."

The attack came days after President Pervez Musharraf, a US-backed military ruler, fuelled Islamist anger with an army assault on the pro-Taliban mosque complex in Islamabad that left 86 dead, most of them militants.

Thousands of Islamic protesters Friday called for Jihad (holy war) and burnt effigies of Musharraf and a puppet of "Uncle Sam," the icon of the United States, which has backed Musharraf as an ally in its "war on terror."

Musharraf has warned he would root out extremists and has deployed thousands of extra troops to northwestern border areas with Afghanistan, remote and lawless regions that have become hideouts for the Taliban and al-Qaeda.

"Troops have been deployed in Swat district and in Dera Ismail Khan following instructions by President Musharraf to beef up security to counter the threat of extremist forces in the region," a military official said.

In another attack in North Waziristan Saturday, two soldiers were wounded by an improvised explosive device that hit their vehicle in the town of Bannu.

Another soldier was shot and wounded at a security checkpost just outside Miranshah, where security forces also said they defused two missiles set up to target a military camp in the town.

A local militant commander threatened "guerrilla war" against the military in the tribal region over setting up of new check posts last week and issued a Sunday deadline for them to leave the posts.

Speaking from an undisclosed location, the pro-Taliban militant accused the government of violating a peace deal signed with tribes and militants last September despite heavy criticism from Western allies and Afghanistan.

"If the government troops do not vacate the checkposts by July 15, we will end the existing peace agreement with the government and launch a guerrilla war," Farhad told AFP by telephone.

Two suicide blasts killed eight people on Thursday, and police Friday said they seized three men and a car packed with seven suicide vests, 100 mortar shells and other explosives in northwestern Dera Ismail Khan.