A Pakistani health worker administers vaccine drops to a child during a door-to-door polio campaign on the outskirts of Islamabad on Wednesday. Aamir Qureshi/AFP/Getty Images

A bomb rigged to a bicycle hit a police patrol on its way to guard a polio vaccination team in northwestern Pakistan's Khyber Pakhtunkhwa province on Wednesday, killing six policemen and a boy, police officials said.

The attack in the Charsadda district also wounded 11 people, four of them policemen, said Officer Shafiullah Khan. The bomb, set off by remote control, struck close to a busy town market, he said. The boy who was killed along with the policemen in the patrol was just a bystander, Khan added.

The vaccination campaign was suspended after the attack, and heavy contingents of police were deployed.

The bombing comes a day after three health workers were killed in an attack on a polio vaccination team in the southern port city of Karachi.

No one immediately claimed responsibility for the latest attacks, but the Pakistani Taliban have killed thousands of civilians, policemen, soldiers and officials in recent years while campaigning to overthrow the government and install their brand of Sharia rule.

The group opposes vaccinations against polio and considers such campaigns a cover for spying against Pakistan and a conspiracy to make Muslim boys sterile.

The incidents are the latest in a surge of violence stretching across Pakistan that has killed more than 100 people this month and left many questioning whether the government has a plan to tackle the country's militancy problem.