Paramilitary police and soldiers swarmed Nigeria's capital Thursday ahead of the ruling party's convention, where delegates will pick the candidate expected to become the next leader of Africa's most populous nation.
The party is choosing between President Goodluck Jonathan and former Vice President Atiku Abubakar, highlighting the religious and ethnic fault lines running through this oil-rich nation of 150 million.
Jonathan, a Christian from the south, became president only after the death of Nigeria's elected leader, a Muslim from the north who had only served one term. For that reason, some within the party believe its presidential candidate should be another northerner.
The voting is to take place Thursday evening and is expected to last well into the night. The winner is expected to go on to victory in the April election.
Since the hand over in 1999 from military rule to a civilian government, Nigerian politics have been dominated by the ruling People's Democratic Party. The party's operatives have the political connections, money and muscle necessary to control Nigeria's unruly and corrupt electoral system.
Security was tight on Thursday in Abuja, where car bombings during an October independence celebration killed at least 12 people and wounded dozens more. Another bomb tore through an open-air beer garden in the city on New Year's Eve, killing at least four people.
Federal police spokesman Olusola Amore said more than 17,000 officers were on hand for the primary convention. On Wednesday night, officials sealed off major roads crisscrossing the arid capital and paramilitary police with night-vision goggles monitored traffic.
On Thursday, roads were blocked off as far as one mile (two kilometers) from the convention. Delegates, supporters and media had to go through at least four different searches, bags were X-rayed, and bodies were patted down and scanned with metal detector wands.
In an unusual order, Amore said the federal police force had told its officers they wouldn't be able to carry firearms, grenades and tear gas canisters into Eagle Square, the convention site.
Before the convention began, the U.S. Embassy in Abuja also warned its citizens "to exercise caution and avoid areas where there are political or other large public gatherings" during the election season.
Every major ministry office was shut down for the day.
Jonathan's decision to contest the election brought anger from northern leaders fearful of being cut out of the lucrative position of president in a nation fueled by billions of dollars of oil revenues. Abubakar, a former Customs officer who created an oil and gas empire before becoming vice president, was chosen as a consensus candidate of the northern elite.
Another minor candidate, Sarah Jubril, will be included on the party's ballot.