Tuesday, June 9, 1998 Published at 13:35 GMT 14:35 UK
New Nigerian military ruler
Gen Abubakar signing documents at his swearing-in, shown on Nigerian TV
Listen to a 30 minute radio special from the BBC African Service: 'After Abacha'
The new head of state in Africa's most populous nation is the defence chief, Major-General Abdusalam Abubakar.
He was chosen by Nigeria's Provisional Ruling Council at a late-night session after the burial of General Abacha, who died suddenly in the early hours of Monday, leaving a potential power vacuum.
Nigeria's main opposition group, the United Action for Democracy, has rejected the appointment and has said it will go ahead with demonstrations on Friday calling for the end of military rule.
A leading dissident, the Nobel laureate Wole Soyinka, said the world must put pressure on Nigeria to enact democratic reforms.
"All hands must be on deck to move this nation forward. I will address the nation in due course," he said.
The new head of state made no mention of presidential elections looming on August 1 for which his predecessor was the sole candidate.
Correspondents say General Abubakar will have to decide whether to hold presidential elections planned for August, and whether to release political opponents of Mr Abacha.
The new leader declared a week of national mourning from Tuesday in honour of Abacha. Flags will be flown at half mast on all public buildings.
General Abacha, who reportedly died of a heart attack, left no constitutional replacement.
His former deputy, Lieutenant-General Oladipo Diya was sentenced to death in April for plotting to take power, and the post was never filled.
But the chairman of the opposition National Democratic Coalition of Nigeria (NADECO) said that whoever succeeded General Abacha should respect the scheduled transition to civilian rule.
Promises of civilian rule
Government members portrayed him as the only man who could unite such a diverse nation.
But his opponents in Nigeria saw him as part of a military elite desperate to hang on to power.