The retired general - who was imprisoned by former military dictator Sani Abacha - is now the favourite to win presidential elections on 27 February, the latest step on Nigeria's return to civilian rule.

Mr Obasanjo, who held power between 1976 and 1979, stands out as Nigeria's only military ruler voluntarily to have handed over power to elected civilians.

Barnaby Phillips in Lagos: "Mr Obasanjo says he will put right years of misrule"

The current military leader, General Abdulsalami Abubakar, has pledged to step down on 29 May after handing over power to the first civilian president in 15 years.

Officials said Mr Obasanjo took nearly 1,700 votes from the 2,469 delegates at the Peoples' Democratic Party (PDP) convention in the central town of Jos.

His supporters, who had stayed up all night to watch the voting, immediately began celebrating in the streets surrounding the convention stadium.

In second place, with more than 520 votes, was former civilian Vice-President Alex Ekwueme.

All three of Nigeria's parties must submit the names of their candidates for the presidential election on Monday.

The All Peoples' Party, Nigeria's second largest party, has named Ogbonnaya Onu as its presidential candidate. The low profile candidate is a former governor of eastern Abia state.

Barnaby Phillips: Critics of the former general say his military links are too close

The smaller Alliance for Democracy has also chosen its candidate, former Finance Minister, Olu Falae.

Under an electoral pact the two smaller parties are expected to field a single presidential candidate to stand against Mr Abasanjo.

Jail sentence

Mr Obasanjo and 43 other soldiers and civilians accused of plotting a coup against the late General Abacha were handed lengthy jail terms by a special court martial in 1995.

When General Abubakar took over as head of state following the unexpected death of General Sani Abacha, he released nine key political prisoners, including Mr Obasanjo, in June 1998.

An exclusive interview with General Obasanjo in June 1998

Mr Obasanjo initially said he would not run again for the country's top office but in November last year announced he had changed his mind after consultations with friends and supporters.

He is an ethnic Yoruba from south west Nigeria and correspondents say he enjoys the backing of many in the Hausa-speaking north, which has dominated Nigerian government for decades.

He also has the support of many retired and serving military officers.