Nigeria's former military ruler Ibrahim Babangida has announced he will be a candidate in the presidential election due to be held in April 2007.
Babangida said the challenge was to make Nigeria whole
In a press interview, he accused the country's present political elite of fuelling ethnic and religious violence.
Mr Babangida governed Nigeria for eight years until 1993.
He was toppled from power by mass protests after he annulled elections that were widely seen as having been won by a businessman, Moshood Abiola.
"I will contest in the election. Under the banner of the Nigerian people," Mr Babangida said in an interview with Reuters and the London newspaper the Financial Times.
Mr Babangida is a member of the ruling People's Democratic Party (PDP), but it is far from certain whether the party would back him as its presidential candidate.
Vice-President Atiku Abubakar is also believed to be seeking the PDP nomination.
"The challenge of the next leadership is to make Nigeria whole again," Mr Babangida said, blaming the political elite for fuelling violence that has killed at least 15,000 people since democracy was restored to Nigeria in 1999.
He dismissed suggestions that current President Olusegun Obasanjo would try to remain in power beyond his two-term constitutional mandate.
"As long as we conduct elections, which I am optimistic that we will in 2007, the transition process from civilian to civilian is feasible, it's workable," Mr Babangida said.
"We have a constitution. If you go outside that, it is like a breach."
Correspondents say there has been speculation in Nigeria that Mr Babangida gave financial support to Mr Obasanjo's 1999 election campaign, in return for a promise that he would become the president's chosen successor.
Mr Obasanjo has however denied favouring any particular successor to the presidency.
The BBC's Mannir Dan Ali in Abuja says Mr Babangida is likely to receive support across the political spectrum as he has financially backed many other elected politicians.
But there are several obstacles that may yet block his path back to the presidency, our correspondent says.
The widow of Gen Mamman Vatsa, who was executed during Mr Babangida's time in office for plotting a coup, is calling for an investigation into his death.
While an anti-corruption body is questioning his son's ownership of a local telecommunication's company.