Gunmen on a motorcycle have shot dead a police officer protecting polio workers during a UN-backed vaccination campaign in Pakistan.
The attack took place as dozens of polio workers - including several women - were going door-to-door to vaccinate children in Gullu Dheri village of Swabi district in Khyber Pakhtunkhwa province.
"The polio workers were terrified and immediately went back to their homes after the attack," a police spokesman said. "The anti-polio drive in that village has been suspended."
Elsewhere in the north-west, a man wounded a polio worker with an axe. He was marking houses in Machi village to indicate where vaccines had been administered and the attacker became angry after his door was marked.
The attacks occurred on the second day of a three-day campaign against polio that was launched by the provincial government. No one claimed responsibility for the shooting in Gullu Dheri, but suspicion fell on militants.
Some Islamic militants oppose the vaccination campaign, accuse health workers of acting as spies for the US and claim the polio vaccine is intended to make Muslim children sterile.
Suspicion of vaccination campaigns heightened considerably after a Pakistani doctor helped in the US hunt for Osama bin Laden.
In December, gunmen killed nine polio workers in similar attacks across Pakistan, prompting authorities to suspend the vaccination campaign in the troubled areas. The UN also suspended its field operations in December as a result of the attacks. They have since resumed some field activities.
The latest campaign in Khyber Pakhtunkhwa was launched on Monday to give oral drops to those children who had missed it the first time round.
Pakistan is one of only three countries where the crippling disease is endemic. The virus usually infects children living in unsanitary conditions; it attacks the nerves and can kill or paralyse. As many as 56 polio cases were reported in Pakistan during 2012, down from 190 the previous year, according to the United Nations.
Most of the new cases in Pakistan were in the north-west, where the presence of militants makes it difficult to reach children.
Pakistan is also struggling to maintain control of its southern province of Baluchistan.
Gunmen in a car opened fire on two police constables who were patrolling on motorcycles in the provincial capital, Quetta. Both the officers were killed instantly.