The location of the gathering was strategically chosen after a north-south rift within the ruling party led to a divisive primary campaign eventually won by Jonathan, a southern Christian.

His Peoples Democratic Party sought to put divisions behind it ahead of the April 9 election in Africa's most populous country, and Jonathan spoke of reforming the economy and improving Nigeria's erratic electricity supply.

"There must be power everywhere," Jonathan said, with outages daily occurrences despite the country's oil wealth.

He also addressed security, with Islamist attacks in the country's north and clashes between Christian and Muslim ethnic groups in the centre raising major concerns ahead of the vote.

Bomb attacks have also hit the central city of Jos and the capital Abuja in recent weeks.

The oil-producing Niger Delta region, the repeated site of militant attacks in recent years, has been relatively calm, but observers have warned violence could again flare up there.

"For every bomb detonated, we will pursue you until we get you," Jonathan said.

Jonathan is favoured to win the election in Africa's largest oil producer after defeating a challenge from the mainly Muslim north to take the ruling party nomination.

His PDP has won every presidential vote since the country returned to civilian rule in 1999.

There has been talk of his main opponents, including an ex-military ruler, forming an alliance, but they have so far failed to reach a deal.

Monday's rally was held in a 15,000-seat stadium in the symbolic city of Lafia -- once the seat of a centuries-old kingdom -- in the so-called middle belt between the north and south.

The neighbouring state of Plateau has been hit by repeated clashes between Christian and Muslim ethnic groups that have killed scores of people.

Such ethnic, religious and regional divisions are likely to play a continuing role in the run up to the vote.

Jonathan emerged as the PDP candidate last month, upsetting an internal party arrangement that sees power rotated between the north and south every two terms.

He is the first head of state from the Niger Delta and came to power last year after the death of president Umaru Yar'Adua, a northerner who had not yet finished his first term.

High-profile politicians from the north had opposed the candidature of Jonathan on grounds that Yar'Adua died before he completed the term alloted to their region.

The rule is variously viewed as an outdated policy pandering to ethnic politics and a power-sharing deal helping to hold together the vast country of 150 million people.

Jonathan enjoys the backing of the majority of the country's powerful state governors. He has reportedly told supporters he would serve only one term if he wins -- widely believed to have been offered as a concession in his negotiations with the governors.

At the moment, he faces a limited challenge from a fragmented opposition.

"By the grace of God, these evil machinations against our party have failed," acting party chairman Haliru Mohammed Bello told the rally.

His main challengers include former military ruler Muhammadu Buhari, representing the Congress for Progressive Change, and ex-anti corruption czar Nuhu Ribadu of the Action Congress of Nigeria, the most prominent opposition party.

Nigeria's last elections in 2007 were considered deeply flawed by local and international observers, but Jonathan has pledged to ensure a credible vote this time around.

Legislative and state ballots will also be held in April.