igeria has launched an investigation into the conduct of a "considerable number" of military officers, a presidential official told AFP, amid claims that disaffected soldiers in the oil-exporting west African giant may be canvassing support for a coup d'etat.

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"It's true that the intelligence community -- national and military security agencies -- are investigating what looks like a serious breach of security on the part of some military officers and apparent civilian collaborators," said President Olusegun Obasanjo's spokeswoman, Remi Oyo.

Asked to confirm reports from military sources that 28 officers had been interrogated in recent days as part of the investigation, Oyo said: "I cannot say the exact figure, but it's a considerable number."

"But it remains an investigation on an allegation and the intelligence community is just doing its job, so there is nothing that is extraordinary about what is happening. It is the duty of the intelligence community to investigate all allegations and apparent security breaches," she said.

Officials played down fears that Africa's most populous country could be on the verge of its sixth military takeover since 1966, and just five years after emerging from its last bout of brutal dictatorship, insisting that the officers allegedly involved posed no threat.

But any hint that the world's sixth largest oil exporter might be verging on another round of political instability will raise deep concerns at home and among the international community.

An army general, who spoke to AFP on condition of anonymity, said most of those questioned were disaffected elements who did not have current commands and, while being potential troublemakers, were no threat to the government.

Another officer said the men had been questioned and released, pending further investigations.