KANO, Nigeria — Police in northern Nigeria arrested and charged two radio journalists and a local cleric alleged to have sparked the killings of at least nine women gunned down while trying to administer polio vaccines, officials said Tuesday. Police asserted that their on-air comments about a vaccination campaign in the area inflamed the region and caused the attacks.

The allegations against the journalists working for Wazobia FM show the continuing struggle over free speech in Nigeria, a nation that came out of military rule only in 1999 and where simply taking photographs on the street can get a person arrested. Though Nigeria has a rambunctious free press, threats and attacks against journalists remain common, and unsolved killings of reporters still haunt the country.