ABUJA (Deutsche Presse-Agentur) -- Unknown gunmen killed nine people in two shootings in the northern Nigerian city of Kano, in an apparent attack on polio vaccination campaigners.

Kano police spokesman Ibrahim Majiya said three additional people were being treated for injuries at a hospital.

A polio immunization campaign kicked off this week.

Nigeria is one of the last places in the world where polio is still endemic. Some Muslim clerics have voiced opposition to vaccination campaigns.

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