Elsewhere in the region, four soldiers and 10 militants were killed in a checkpoint shootout.
The attacker rammed an explosive-laden car into another vehicle near a bus packed with passengers in Parachinar, a town in the North West Frontier Province, said Mohammed Kamal, a local police official.
"According to our information, it was a homicide attack, and the body parts of the attacker are being collected," Kamal said.
Sahabzada Mohammed Anis, the top government official in the town, said the dead and injured were rushed to hospitals in Parachinar, about 150 miles south of the provincial capital of Peshawar.
Mohammed Sultan, a doctor at the Parachinar Hospital, said they received five bodies after the blast, and that four of the injured died later. At least two other victims were still in critical condition, he said.
In the other attack Saturday, pro-Taliban militants assaulted a security checkpoint in Oblanki, a remote area of the North Waziristan tribal region, triggering a shootout that killed four soldiers and 10 militants, officials said. Five other soldiers were wounded, said army spokesman Maj. Gen. Waheed Arshad.
The security situation in Pakistan, especially in the tribal zone bordering Afghanistan, has been deteriorating for weeks, and almost daily attacks have killed more than 300 people.
Pakistan is a key ally of the United States in its war on terror, and it has deployed about 90,000 soldiers in its tribal regions since the Sept. 11, 2001, attacks to flush out remnants of the Taliban and Al Qaeda, who are believed to be hiding there.
President Gen. Pervez Musharraf is under increasing pressure from Washington to crack down in the tribal region.
The surge in violence has followed tribal leaders' withdrawal from a 2006 peace deal with the government, and amid widespread anger at an army raid of Islamabad's radical Red Mosque last month that left at least 102 people dead.
Arshad said Saturday's gunbattle raged for two hours and ended when the militants fled to nearby mountains with some of the bodies of slain associates.
A local intelligence official, speaking on condition of anonymity because he was not authorized to speak to media, said the assailants shouted "God is great" and used rockets, assault rifles and other munitions to target the checkpoint.
Two helicopter gunships were used to pursue the fleeing fighters, he said
Separately, militants fired eight rockets at a security checkpoint near Miran Shah, the main town in North Waziristan, but caused no damage or casualties, the official said.
Pakistan used to be a main supporter of Afghanistan's former Taliban regime, but Musharraf switched sides after the attacks in the U.S. He has since said that his fight against terrorism would continue until it is reasonably assured that militancy, extremism and terrorism have been defeated.