By Alex Last
BBC News, Lagos
The leader of one of Nigeria's two main opposition parties has called for a grand opposition alliance to defeat the ruling party in this month's elections.
Gen Buhari is a former military ruler of Nigeria
General Muhammadu Buhari has called a meeting of opposition parties on Thursday to discuss his proposal.
The other main opposition leader, Vice-President Atiku Abubakar, is battling in court to be allowed to run.
Parliamentary and state governor elections are due this Saturday, with the presidential contest a week later.
Officials from Mr Abubakar's Action Congress say their representatives will attend the meeting.
It is not the first time there has been talk of an opposition alliance.
But this is the last chance for the opposition to come together to try to stop the powerful governing party.
Opposition officials say co-operation is crucial to ensure a free and fair election and stop vote-rigging.
It is not clear if Atiku Abubakar will be allowed to stand
But when it comes to agreeing on a single opposition candidate it gets a lot more tricky.
It seems unlikely that an alliance will come into play in the legislative and gubernatorial elections, where candidates from all parties look set to battle it out.
The key question is whether they can reach an agreement on the 21 April presidential election.
General Buhari is a rather popular former military ruler, but his All Nigeria People's Party lacks money and the structures needed to translate popularity into results.
The vice-president has the money and a stronger political network, so together they could present a much tougher challenge to the governing party.
But it is far from certain that a deal will be struck.