The bomber attacked police Sunday while they were investigating a minor blast in the town of Dera Ismail Khan near the Afghan border, said Sanaullah Khan.
Five police officials and two civilians were killed by the second blast and 16 police were among the wounded, Khan said.
Amanullah Khan, a wounded police official, said he and his colleagues were attending to four civilians injured by the first explosion when the bomber attacked.
“When I stood up, there was blood everywhere,” said Khan. “My colleagues were crying with pain.”
Local television showed smoldering bicycles, broken furniture and torn police uniforms splattered with blood littering the ground in front of shops destroyed in the attack. The footage also showed a police van damaged by the blast.
“This is the work of anti-state and anti-Islamic forces,” said local parliamentarian Khalifa Abdul Qayoum. “We are not afraid of them. We will fight them.”
Following the attack, unknown gunmen opened fire on an ambulance carrying one of the dead back to his home village, wounding three people, said police official Jehangir Khattak.
Many Al Qaida and Taliban militants fled to northwest Pakistan from Afghanistan after the US-led invasion in 2001. The militants have regrouped and have been launching attacks against Western forces across the border in Afghanistan and against security forces and civilians inside Pakistan.
During a raid elsewhere in northwest Pakistan on Sunday, the army discovered a van packed with 880 pounds (400 kilograms) of explosives. The van was intended to be used in a suicide bombing, the army said.
Six suspected militants were arrested in the raid on a house in the Khyber tribal region, the army media center said. The army also found suicide jackets, rockets, assault rifles and improvised bombs in the house.
The army has been in Khyber trying to secure the main supply route for US and Nato forces in Afghanistan. Information from militants arrested during the operation led to Sunday’s raid, said the army.