Police in Nigeria raided a newspaper office Wednesday after detectives arrested four journalists over the publication of a purported letter from the nation's former president instructing its current leader to fire government officials.

Police descended on the Abuja office of The Nation newspaper as reporters working there fled onto nearby streets, said the journalists who spoke on condition of anonymity out of fear of being arrested. Officers apparently were searching for material to identify the source that gave the newspaper the alleged letter from former President Olusegun Obasanjo to President Goodluck Jonathan.

Detectives arrested four journalists from the newspaper Tuesday after failing to find the publication's senior leadership at its Lagos office, a statement from its general editor said.

"The police invasion, apparently meant to decapitate the paper's leadership and disrupt production of the Wednesday edition, paralyzed work at the newspaper house for many hours and unsettled staff," read the statement from Kunle Fagbemi, one of those supposedly wanted by the police.

Police officials in Lagos and Abuja could not be reached for comment Wednesday.

The small daily newspaper, one of many publishing in Nigeria's unruly and outspoken free press, blamed the harassment on an Oct. 4 front page story about the letter. The newspaper alleged the letter outlined Obasanjo's desire for Jonathan to replace the leaders of the Petroleum Technology Development Fund and four other agencies with his own candidates.

The letter has hit a nerve in Nigerian politics, as it recommends replacing leaders from the Muslim north as opposed to the country's Christian south, where Jonathan and Obasanjo come from. Some also view Jonathan as beholden to Obasanjo's interests, so the letter raises new concerns about Jonathan's independence as a leader.

Obasanjo denied the authenticity of the letter and threatened legal action, but the newspaper said it stood by its story.

Attacks against journalists remain common in Nigeria, a country of 150 million where corruption pervades government and business. Reporters found themselves routinely targeted during military rule of Africa's most populous nation as well, though 12 years of democracy in the nation have enshrined a belief, if not an absolute right, to free speech.

However, many reporters accept cash payments from interview subjects or "brown envelope" bribes slipped into briefing materials at news conferences. Major politicians also finance newspapers to influence their coverage.

Mohammed Garba, president of the Nigeria Union of Journalists, described the arrests and raids Wednesday as a means to silence journalists who uncover unflattering facts in a nation pervaded by backroom deals.

"We condemned the act and we feel it is wrong for government or the security agencies to launch an attack on the press," Garba told the AP. "If our colleagues have committed any offense, there is a court of law. We expect that they would take them to court and the issue can be squarely addressed by the courts."

4 Nigeria newspaper reporters arrested over story