The BBC's Barnaby Phillips in Lagos: The commission faces a daunting task

The commission, headed by retired Justice Chukwudifu Oputa, was initially appointed to investigate abuses during 15 years of military rule, which ended when President Obasanjo took office as elected president on 29 May.

The decision follows demands for a thorough investigation of rights abuses in Nigeria since independence in 1960.

In 1966, soldiers overthrew the elected government and the country slid into turmoil leading to a bloody civil war when Biafra attempted to secede in 1967.

More than a million died in the war, which lasted until 1970.

There have been complaints recently that abuses of the period, including reports of massacres, had never been investigated.

Most of those whose regimes will be investigated are still alive and some still wield considerable power in Nigeria.

Indeed, the the panel will be required to examine human rights abuses when President Obasanjo was in power previously as a military ruler from 1976 to 1979.

A Biafran soldier in the 1967-70 civil war

President Obasanjo, a hero in the war against secessionist Biafra, emerged as military ruler after General Murtala Mohammed was assassinated in office in 1975.

He voluntarily handed over to elected civilians in 1979, but soldiers again seized power four years later.

International precedents

Justice Oputa said that the seven-member panel, which was last month formally sworn in and given powers to subpoena witnesses, was still in the process of working out a budget for its investigations.

"The panel and the government must not underestimate the scale of the task we are taking on," he said.

The comission last week held a meeting with experts from South Africa, Chile, Guatemala and Argentina, which have all held probes of human rights abuses in the past.

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

"We will look to produce a general survey of what has gone wrong in Nigeria, as well as investigate specific cases of rights abuses."

He said it was possible that the first public hearings would now have to be postponed until the new year.

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