A Pakistani health worker has been shot and injured in Peshawar, the latest in a spate of attacks against a polio vaccination drive in the country.

On Tuesday, a UN-backed programme to eradicate the disease was suspended in Karachi after four female health workers were shot dead in the city.

No group has said it carried out the shootings, but the Taliban have issued threats against the polio drive.

Pakistan is one of just three countries where the disease is still endemic.

In Wednesday’s attack, gunmen opened fire on a team of four men administering polio vaccinations in Peshawar, critically injuring one, doctors told Reuters news agency.

It came a day after a female worker died after an attack in the north-western city.

Prime Minister Raja Pervez Ashraf on Tuesday condemned the attacks and praised the work of the polio vaccination teams, calling on regional authorities to guarantee their safety.

Wednesday is the final day of a three-day nationwide anti-polio drive – during which an estimated 5.2 million polio drops were to be administered.

There has been opposition to such immunisation drives in parts of Pakistan, particularly after a fake CIA hepatitis vaccination campaign helped to locate Osama Bin Laden in 2011.

Militants have kidnapped and killed foreign NGO workers in the past in an attempt to halt the immunisation drives, which they say are part of efforts to spy on them.

Afghanistan and Nigeria are the only other countries where polio is still endemic.

Pakistan is considered the key battleground in the global fight against the disease, which attacks the nervous system and can cause permanent paralysis within hours of infection.

Almost 200 children were paralysed in the country in 2011 – the worst figures in 15 years.

Earlier this year, the Global Polio Eradication Initiative warned that tackling the disease had entered “emergency mode” after “explosive” outbreaks in countries previously free of polio.

The World Health Organization (WHO) said polio was at a tipping point, with experts fearing it could “come back with a vengeance” after large outbreaks in Africa and Tajikistan and China’s first recorded cases for more than a decade.

Declaring polio a national emergency, the Pakistani government is targeting 33 million children for vaccination with some 88,000 health workers delivering vaccination drops.