Things are getting better... There is much less despair in the air.

Olusegun Obasanjo

The 65-year-old leader ended weeks of speculation by saying he had made the decision to stand after "lengthy consultation with family, friends, critics and allies."

Mr Obasanjo came to power in 1999, in elections that put an end to 15 years of military rule.

He at first won support for his tough stand against corruption, but more recently his government has been criticised for its human rights record, and for its handling of the economy.

But as he launched his campaign at a rally in the capital, Abuja, Mr Obasanjo said his critics were wrong.

Dark days

He said the nation was "in despair" when he took over.

Announcing his intention to run again, he said: "things are getting better". There are more cars on the roads, more aircraft in the skies, the country's ports are busier, there are more jobs and "living conditions continue to improve."

Nigerians queued to vote in the last election

Mr Obasanjo said he would once again seek the nomination of the People's Democratic Party.

The BBC's Dan Isaacs in Lagos says that despite the perceived failing of the government to improve living standards or tackle violence, few in Nigeria would welcome a return to the dark days of military rule.

If the elections due next year pass off peacefully, Mr Obasanjo will be the first civilian leader of Nigeria to conduct a successful vote since independence in the 1960s.

Our correspondent says that ironically, military governments in Nigeria have proved better at organising elections than civilians.

The last attempt almost two decades ago was deeply flawed and swiftly followed by a military coup.

Mr Obasanjo had a previous stint as military ruler in the 1970s.

Power base

Although a Christian southerner, he has had significant support amongst northern Muslims, an achievement which won him the presidency three years ago.

Up to 10,000 people have died in Nigerian clashes

This time, our correspondent says a strong northern opponent might be able to undermine that power base.

In the past two years, the adoption of Sharia law by most northern states has led to violent clashes between Christians and Muslims.

Meanwhile another former Nigerian military ruler has announced that he plans to seek the backing of a political party.

Muhammadu Buhari has said that he intends to register with the opposition All People's Party - a step towards standing in next year's presidential election.