Two Nigerian journalists have been arrested over the killing of nine female polio vaccinators in northern Kano state on Friday, police have said.
Kano police chief Ibrahim Idris told the BBC the journalists would be charged with culpable homicide.
They had incited the public to oppose vaccinations through their Wazobia FM radio station, he alleged.
Some Muslim leaders in northern Nigeria believe polio vaccinations cause infertility among women.
They see it as a Western conspiracy to reduce the Muslim population.
Such opposition is a major reason why Nigeria is one of just three countries where polio is still endemic.
There were 121 cases of polio in Nigeria last year, compared to 58 in Pakistan and 37 in Afghanistan, according to the Global Polio Eradication Initiative.
No group has said it carried out Friday’s two separate attacks on the polio vaccinators.
Some have accused Islamist militant Boko Haram of the killings but the group has not commented on the allegations.
In the first attack in Kano, vaccinators were shot dead by gunmen who drove up on a motor tricycle.
Thirty minutes later gunmen targeted a clinic outside Kano city as the vaccinators prepared to start work.
Mr Idris told the BBC the journalists had incited the public to reject polio immunisation, in a programme broadcast two days before the attacks.
Wazobia’s station chief Sanusi Bello Kankarofi told AFP news agency that a presenter and a reporter were being held by Kano police, along with a man who featured on their programme.
A third journalist had been released after being questioned, Mr Kankarofi said.
Wazobia’s popular Sandar Girma programme focused on a man who was allegedly forced to submit his children to vaccinations by district officials, AFP reports.
The children’s father is among those being held, it quotes Mr Kankarofi as saying.