A Nigerian newspaper says police have arrested five of its journalists after the paper published a controversial story on its front page last week.

The Nation newspaper says that Nigerian police on late Tuesday arrested five senior journalists and two other employees from its Lagos and Abuja offices.

The paper said it believes the arrests were “not unconnected” to its October 4 cover story, which contained a “secret” letter allegedly written by former Nigerian president Olusegun Obasanjo.

In the letter, Mr. Obasanjo is said to have requested current President Goodluck Jonathan replace certain government officials at Nigeria's Petroleum Technology Development Fund, an agency that trains local workers in the country's valuable oil and gas industry.

Mr. Obasanjo denies writing the letter, and has threatened legal action against the paper.

Nigerian police have not officially confirmed the arrests.