Nigeria's president-elect has said he will reform the election process, which observers strongly criticised during last month's poll.
Umaru Yar'Adua won by a landslide, according to official results
Umaru Yar'Adua said he would review April's elections, which he controversially won.
Local observers said the polls were a "charade" with results announced in areas where no voting took place.
Mr Yar'Adua is due to be sworn in on Tuesday. The two main losing candidates have challenged the results in court.
Meanwhile, the European parliament has urged the European Union to withhold financial aid from Nigeria, until new elections are held, reports the AP news agency.
EU election observers said the polls were "not credible".
Mr Yar'Adua said he would set up a committee of eminent Nigerians to recommend changes to the electoral law.
He made the promise after meeting one of the ruling People's Democratic Party (PDP) founders, Alex Ekwueme.
Muhammadu Buhari has challenged the results in court
He urged Nigeria's new leader to reconcile Nigerians.
Muhammadu Buhari and Atiku Abubakar on Wednesday both urged the courts to nullify the elections.
The opposition accuses the election commission of being biased towards the PDP.
As they filed their legal papers, a group of 48 Nobel laureates, including 1986 literature prize winner Wole Soyinka, also called for new elections within 18 months.
"We are concerned that the new government's lack of legitimacy increases prospects for violent conflict with serious consequences for Nigeria and the region," they said.
The EU said at least 200 people were killed in poll related violence this year.
In some cases, PDP militants took control of polling stations.
Nigeria's main trade grouping has called for strikes next Monday and Tuesday.
But previous opposition calls for protests have not been widely heeded.