Kano, Nigeria - Gunmen on motorbikes shot dead nine health workers who were administering polio vaccinations in two separate attacks in Nigeria's main northern city of Kano on Friday, police said.
No one claimed responsibility but Islamist militant group Boko Haram - a sect which has condemned the use of Western medicine - has been blamed for carrying out a spate of assaults on security forces in the city in recent weeks.
The shootings will hit efforts by global health organisations to clear Nigeria of polio - a virus that can cause irreversible paralysis within hours of infection.
“Gunmen opened fire on a health centre in the Hotoro district killing seven, while an attack on Zaria Road area of the city claimed two lives,” said police spokesman Magaji Musa.
“They were working for the state government giving out polio vaccinations at the time of the attack,” Musa added.
Boko Haram killed hundreds last year in its effort to impose Islamic law, or sharia, on a country of 160 million split roughly equally between Christians and Muslims.
The group is seen as the most serious threat to the stability of Africa's top energy producer, and Western governments fear the country could become a base for operations of al-Qaeda-linked Islamist groups in the Sahara.
President Goodluck Jonathan has highlighted links between Boko Haram and Saharan Islamists and said that relationship justified his decision to join efforts by French and West African forces to fight militants in Mali last month.
In 2003, northern Nigeria's Muslim leaders opposed polio vaccinations, saying they could cause infertility and Aids.
Their campaign against the treatments was blamed for a resurgence of the disease in parts of Nigeria and other African countries previously declared polio-free.
Polio, a virus that attacks the nervous system, crippled thousands of people every year in rich nations until the 1950s.
At least 16 health workers taking part in polio vaccination drives have were killed in a series of attacks in Pakistan in December and January.
Local Taliban militants said they did not carry out those attacks although its leaders have repeatedly denounced the vaccination programme as a plot to sterilise people or spy on Muslims. - Reuters