A police officer says a bomb exploded in northwest Pakistan near a vehicle carrying officials taking part in an anti-polio campaign, killing at least six people.

Police official Samiullah Khan says Monday morning's bomb killed four police officers and two members of a local peace committee riding in the van.

Khan says the bombing happened in the village of Malikhel, outside the provincial capital of Peshawar.

Pakistan is one of three countries in the world where polio is still endemic.

Part of the reason that it is still prevalent is that militants who oppose the campaign often target the workers and threaten people who want to get their kids vaccinated.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

The Afghan Taliban are financially supporting Pakistani militants at war with Islamabad and providing sanctuary for them in neighboring Afghanistan, the Pakistani Taliban's spokesman said, highlighting the risk both groups pose to the Pakistani government.

The disclosure, which the spokesman made Saturday in an interview with a small group of reporters, is meaningful because Pakistan has long been accused of pursuing a policy of differentiating between the Afghan and Pakistan Taliban as so-called "good" and "bad" militants _ even though Islamabad denies this.

Pakistan has waged war against the Pakistani Taliban, which seeks to replace the country's democratic system with one based on Islamic law. But it has held off on targeting the Afghan Taliban, which has focused its attacks on U.S.-led troops in Afghanistan. Pakistan has historical ties with the Afghan Taliban, and many analysts believe Islamabad views the group as a useful ally in Afghanistan after foreign forces withdraw.

But the Taliban spokesman's comments illustrate the dangerous nexus between the two groups. This link could become even more dangerous for Pakistan as the U.S. withdraws most of its combat forces from Afghanistan by the end of 2014. That could give the Afghan Taliban more space to operate inside Afghanistan, which could benefit Islamabad's enemies in the Pakistani Taliban.

"The Afghan Taliban are our jihadi brothers," said Shahid in an interview in Waziristan, the Taliban's main tribal sanctuary in Pakistan along the Afghan border. "In the beginning, we were helping them, but now they are strong enough and they don't need our help, but they are now supporting us financially."

The Afghan Taliban are also providing sanctuary for a prominent Pakistani Taliban commander, Mullah Fazlullah, in eastern Afghanistan's Kunar province, said Shahid. Fazlullah was the commander of the Taliban in Pakistan's northwest Swat Valley but was driven into Afghanistan when the Pakistani army launched a big offensive there in 2009.

The army has also staged many offensives in Pakistan's semiautonomous tribal region, the Taliban's main sanctuary, but the militants have proven resilient and continue to carry out regular attacks.

The Taliban have financed many of these attacks through a combination of kidnappings, extortion and bank robberies. But Shahid's comments indicate these sources of financing do not always provide the funds they need.

The government has more recently stepped up efforts to negotiate a peace deal with the Taliban, but those efforts do not appear to be making much progress.

Shahid reiterated the Taliban's view that peace talks will not succeed unless the government releases all militant prisoners and withdraws the army from the tribal region. He also demanded an end to U.S. drone strikes targeting militants in the tribal region.

"Yes, we are terrorists, but we are against the system of the infidels," said Shahid. "We will fight up to our last drop of blood to impose Shariah (Islamic) law in the country."

The interview took place in a guest room attached to a mud house. The Taliban requested that the reporters not reveal exactly where in Waziristan the house was located. Shahid arrived at the house surrounded by bodyguards in a vehicle with tinted windows. He wore white, traditional baggy clothing known as shalwar kameez and a green army jacket. One of the pockets contained a grenade.

After the interview, the reporters were served a meal of beef curry, rice, fruit and cold Pepsi and Mountain Dew.