ABUJA (Reuters) - A group of Nigerian writers, intellectuals and media figures called on President Muhammadu Buhari on Friday to stop the persecution of journalists, after an online publication’s news staff was briefly detained.

Nigerian police late on Thursday arrested the editor and a reporter for the Premium Times, the rights group Amnesty International said, in a dispute raising concern about press freedom in Africa’s biggest democracy. The two were released later that evening without being charged.

“What we see is a disturbing trend that suggests not just an attempt to criminalize the important work that journalists in Nigeria do, but also a drive to frighten and cower and stop this critical constitutionally mandated work through the aggressive use of the state security apparatus,” said a joint letter to Buhari signed by 10 Nigerian public figures.

The letter called on the president to instruct security services to stop harassing and arresting journalists and insist that police follow the law in arresting and charging suspects “in a timely and transparent manner”.

The Premium Times has angered the military with articles saying dozens of soldiers were missing and the chief of staff was facing an investigation over false asset declaration. The armed forces have accused the paper of libel and defamation, charges the publication denied.

The detainment of editor Dapo Olorunyomi and judicial correspondent Evelyn Okakwu have raised concerns about freedom of the press and the power of the military in Nigeria.

The army said in a statement on Thursday it had begun legal action against the Premium Times over its “failure to retract and apologize over false, subversive and malicious publications against the person of the Chief of Army Staff Lieutenant General Tukur Buratai and the Nigerian Army”.

The articles included stories about soldiers missing in Nigeria’s northeast after clashes with Islamic insurgent group Boko Haram.

In a statement, the news publication said the arrest of its editor and correspondent had been made “based on a petition” by the chief of army staff.

“We call on the federal government to rein in the police and assure Nigerians that we are not living in a military dictatorship,” the statement said.