Speaking on state television, President Obasanjo said Mohammed Abacha was being held in connection with what he described as " heinous crimes."

He did not specify the crimes, but said they were committed during General Abacha's rule.

The government also says that two senior members of the late General Abacha's security team - Major Hamza al-Mustapha and Sergeant Barnabas Mishelia - are in detention and will soon be charged and brought to trial in connection with alleged human rights abuses.

Mohammed Abacha was actually arrested nine days ago - but this is the first time the government has commented on his detention.

Release plea rejected

Earlier this week a court in Abuja turned down a plea from Mr Abacha's lawyer that he be released pending charges, although the court has set another hearing for 18 October.

General Abacha's death last June paved the way for Nigeria's return to democracy.

His successor, General Abdulsalami Abubakar, freed hundreds of people jailed under the Abacha regime including Olusegun Obasanjo who brought 15 years of military rule to an end when he was elected President in May.

When he came to power, President Obasanjo pledged to investigate allegations of corruption and human rights abuses under the military regime.

Allegations of abuses

Earlier this week he ordered the commission investigating human rights violations to extend its probe back to the first military coup in 1966.

That would include the period when President Obasanjo was in power previously as a military ruler from 1976 to 1979.

The panel has so far received more than 11,000 memoranda detailing alleged human rights abuses and now expects many more.

The commission has one year from the date of its first public hearing to complete its work.