ABUJA (Reuters) - Former Nigerian military ruler Muhammadu Buhari on Thursday declared his candidacy for presidential elections in April, pledging to clamp down on corruption and review the country's privatisation plans.
Buhari's reputation as a disciplinarian and a popular perception that he is cleaner than many in the political elite could make him the main opposition candidate to run against the ruling People's Democratic Party (PDP) nominee.
President Goodluck Jonathan is broadly considered the front runner in the ruling party primaries, due by mid-January, but faces a tough battle against former Vice President Atiku Abubakar.
Buhari, the military ruler of Africa's most populous nation for 20 months between 1983-85, lamented what he described as "pervasive corruption" in the years since the end of military rule just over a decade ago.
The PDP candidate has won every election since then.
"Alas, after almost 12 years of our democratic experience, the administration's record is a catalogue of betrayal and thoroughly squandered opportunities," Buhari said in a speech announcing his candidacy on the platform of the opposition Congress for Progressive Change (CPC) party.
He said Nigeria should be a democratic example in the West African region, leading its economic progress.
Buhari came to power in 1983 in an almost bloodless New Year's eve coup that ended Nigeria's second attempt at democracy. His iron-fisted administration is best remembered for its austerity measures, the jailing of politicians on corruption charges and the execution of drug traffickers.
He was toppled and placed under prolonged detention in 1985 by his then army chief, Ibrahim Babangida, another ex-military ruler who is a potential presidential contender.
Buhari said he would review reforms including privatisation plans, which he said had in the past been marred by corruption.
"The so-called reform programme ... in the last 12 years has been zeroed to privatisation, interpreted to mean 'to strip and sell national assets to cronies at knockdown prices'," he said.
"Its implementation has all the hallmarks of the PDP administration: corruption."
History has favoured the incumbent in previous Nigerian elections, but Jonathan's candidacy is controversial because of a pact in the PDP that power should rotate every two terms between the mostly Muslim north and largely Christian south.
Jonathan is a southerner and inherited office earlier this year when President Umaru Yar'Adua, a northerner, died part way through his first term. Jonathan's opponents say only a northerner, such at Abubakar, can stand as the PDP candidate.
The controversy risks splitting the ruling party and dividing northerners, a situation which could favour Buhari, who is from what is now the northern state of Katsina. Babangida threatened this week to quit the PDP if Jonathan stands.
"The man on the street (in the north) is more in support of General Buhari than any other person," said Shehu Sani, a pro-democracy activist based in the northern city of Kaduna.
"Not only is he from the north, but he seems to be a leader who has never demonstrated ostentatious wealth and is not corrupt," he told Reuters.
Buhari said one of the main tasks of any new government would be to tackle "rampant insecurity", requiring co-ordination between the armed forces, police and civil society.
Nigeria's commercial capital Lagos has a reputation for high crime levels, although the situation has improved considerably in recent years, but kidnappings continue in the Niger Delta oil region and there have been increasing attacks on police and local officials by an Islamist sect in the remote northeast.
Buhari and Abubakar were the main challengers to Yar'Adua in the 2007 polls, marred by widespread rigging, and fought more than a year of legal battles to try to annul his victory.
Buhari also ran against former president Olusegun Obasanjo in 2003 and lost in an election which was also widely condemned as rigged. He spent two years contesting that result in court.