KANO, Nigeria (Reuters) - Three Nigerian journalists have been arrested for inciting violence by saying on a radio show that polio immunizations were an anti-Islam Western conspiracy, just days before health workers administering the vaccines were killed.

Gunmen on motorbikes shot dead the nine health workers in two separate attacks in Nigeria's main northern city of Kano on Friday.

No one claimed responsibility but Islamist militant group Boko Haram, a sect that has condemned the use of Western education, has been blamed for carrying out a spate of assaults on security forces in the city.

Kano Police Chief Ibrahim Idris told Reuters on Monday three journalists from Wazobia FM had been detained after they said on their show on Wednesday that immunization against polio was anti-Islam and a Western conspiracy to cause infertility in women.

Some influential Muslim leaders in Kano openly oppose the vaccinations for the same reasons.

The killings could hamper efforts by global health organizations to clear Nigeria's mostly Muslim north of the virus that can cause irreversible paralysis within hours of infection.

Polio crippled thousands of people every year in rich nations until the 1950s. As a result of vaccination, it is now only endemic in three countries - Nigeria, Afghanistan and Pakistan.

According to the World Health Organisation, there were 121 new cases of polio in Nigeria last year, compared to 58 in Pakistan and 37 in Afghanistan.

In 2003, northern Nigeria's Muslim leaders opposed polio vaccinations, saying then 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.

(Reporting by Chukwuemeka Madu; Writing by Joe Brock; Editing by Alison Williams)