ABUJA (Reuters) - Nigerian police on Tuesday detained a journalist for refusing to reveal the source of an article on a confidential letter from the chief of the force, the reporter’s newspaper said, as Nigeria’s security agencies come under pressure to reform.

The story disclosed a letter from Inspector General Ibrahim Idris to acting president Yemi Osinbajo, Premium Times said. Other media also covered the letter.

President Muhammadu Buhari’s administration has frequently come under fire for constricting press freedoms, and security services have often detained reporters. Nigeria ranks 119th out of 180 countries in Reporters Without Borders’ World Press Freedom Index.

Reporter Samuel Ogundipe’s phone was turned off when Reuters tried to contact him. Nigerian police did not respond to phone calls and messages seeking comment.

Premium Times said its editor-in-chief and another reporter had also been detained but released within a few hours. While in custody, they heard police asking Ogundipe for the source of the letter, the newspaper said.

Another reporter, Jones Abiri, has been in state security service custody since July 2016, appearing in court only this year after two years in detention without trial or family visits.

The chief of Nigeria’s state security service, Lawal Daura, was fired by Osinbajo last week after his agents stopped lawmakers entering parliament, a blockade seen by the opposition as a bid to intimidate its leaders.

Ogundipe reported in the Premium Times that Idris had written to Osinbajo - Nigeria’s vice president, in charge while Buhari takes two weeks’ leave - to say an investigation had concluded that Daura had been behind the blockade.

The police force has also been dogged by problems recently. Osinbajo on Tuesday also ordered the overhaul of a controversial special unit following allegations of repeated human rights violations.