Media playback is unsupported on your device Media caption The blast struck a van near a hospital in the north-western city of Peshawar

Two people, one a police officer, have been killed by a bomb which went off near campaigners against polio vaccinations in Pakistan, say police.

The blast struck a van near a hospital in Budh Bher suburb of the north-western city of Peshawar.

A death toll of six was given earlier but later corrected by police.

Pakistan is one of only three countries where polio remains endemic, due in part to militant resistance to polio mass vaccination campaigns.

Militants have attacked and killed health workers and banned immunisation teams from some areas, forcing hundreds of thousands of children to miss vaccinations.

The other person killed in Monday's attack was a member of a local "peace committee", who opposed the Taliban, and was riding in a van as part of the anti-polio campaign, said police officials.

Polio's last stand? 2012 cases Nigeria - 97

Pakistan - 47

Afghanistan - 26

Chad - 5* Source: IMB * Polio is considered "non-endemic" in Chad Polio killings a major setback

At least 12 people are reported to have been injured. Reports said many were police, but an injured young girl was also pictured in images from the scene.

The team inside the van was supposed to be accompanying the health workers administering polio vaccines in order to protect them, reports said.

One of them, Rasheed Khan, told Reuters news agency: "I was with the polio team. As soon as we reached the front of the hospital... there was a blast right in front of the gate.

"We were around 12 or 13 people."

Police had earlier reported a higher toll but corrected this upon confirmation from medical sources.

Image caption Pictures from the scene showed a young girl injured in the blast

The explosive device was reported to have been detonated remotely.

The Pakistani news website Dawn quoted police as saying another, bigger, bomb had been found in the vicinity of the first one and the bomb disposal squad called in to defuse it.

Pakistan's high commissioner to the UK, Wajid Shamsul Hasan, said the object of such attacks was to gain worldwide publicity "and make the world afraid of coming to Pakistan's assistance when we need... a lot of assistance".

A fake hepatitis vaccination campaign, run covertly by the CIA, helped to locate al-Qaeda leader Osama Bin Laden in 2011. He was then killed in an operation by US Navy Seals.

Since then all vaccination teams have been at greater risk of militant attack.

The Taliban accuse health workers of working as US spies and allege that the polio vaccine makes children sterile.

A rising tide of violence has hindered new Prime Minister Nawaz Sharif's overtures to end the militant insurgency through peace talks with the Taliban.

Peshawar has been particularly hard hit. In just over two weeks, it has suffered four attacks which between them left more than 150 people dead.