LAGOS, Nigeria (AP) — Oil-rich Nigeria's acting leader Goodluck Jonathan was sworn in Thursday as president of Africa's most populous nation, as officials buried the flag-draped corpse of his Muslim predecessor before sundown.

The power shift to Jonathan, a Christian, peacefully ended a profound leadership crisis triggered last November when elected President Umaru Yar'Adua, who died Wednesday at the age of 58, left the country for medical treatment without transferring authority to his deputy.

Jonathan had already assumed presidential powers Feb. 9 after an extraordinary National Assembly vote was called to resolve the leadership vacuum left when Yar'Adua was hospitalized in Saudi Arabia for an inflamed heart.

Nigeria has been plagued by military coups for much of its 50 years of independence, and Jonathan will have to keep a lid on the volatile nation's sectarian divisions as well as oil-industry violence and kidnappings as it edges toward a tense presidential election next year.

Early Thursday, Jonathan put on a sash bearing the green, yellow and white colors of Nigeria, signifying he had formally taken over from Yar'Adua. Jonathan will serve as president through next year's vote, likely to be held by April 2011. He also will be able to select a vice president, whose appointment will be subject to Senate approval.

Soldiers and police officers accompanied Yar'Adua's corpse on a flight Thursday to his home state of Katsina in the country's Muslim north. There, mourners carried his body on their shoulders into a local soccer stadium for a final prayer service. A local imam led the prayers, calling out "God is great" in Arabic and raising his hands to the sky as an anxious and curious crowd jostled around the coffin before it was buried at a cemetery near his home.

In a brief national address, Jonathan promised his administration would focus on good governance during its short tenure, focusing especially on electoral reform and the fight against corruption.

But "one of the true tests will be that all votes count and are counted in our upcoming presidential election," Jonathan said.

An unwritten power-sharing agreement within Nigeria's ruling People's Democratic Party calls for the presidency to alternate between Nigeria's Christians and Muslims. However, Yar'Adua was still in his first four-year term and leaders in the north had expected him to serve two terms.

If Jonathan runs for the office, his candidacy could shatter the ruling party, which has the political muscle necessary to manipulate Nigeria's unruly and corrupt electoral system. Analysts also warn a Jonathan presidential bid could spark fresh violence in a nation of 150 million people split between Christians and Muslims, especially if northern leaders believe they will lose power in the process.

It "creates the room for those who believe the presidency had been assigned to the north by the PDP party," said Charles Dokubo, an analyst at the Nigerian Institute of International Affairs. "As a result, they believe it is the time to fight."

Mark Schroeder, the director of sub-Saharan Africa analysis for STRATFOR, a private security think tank based in Austin, Texas, said, "Jonathan must be interested in contesting for the presidency, but he still has not revealed his hand and he's still pretty hesitant about signaling what his intentions are."

"Jonathan will certainly keep his hat in the ring and that will ensure he remains an influence within Nigeria's political system," he said. "Whether he has enough support (to run for president) ... that's another big question."

Schroeder said Nigeria's political leaders knew they needed to quickly swear Jonathan in as president to show the world there was no power vacuum.

"The U.S. wants political stability in Nigeria so that there's stability in the oil sector," Schroeder said.

Nigeria was the No. 4 oil exporter to the U.S. in February, sending about 896,000 barrels of crude a day to the U.S., outstripping even Saudi Arabia.

Jonathan said peace in the Niger Delta, home to the country's oil industry, remains a priority. Attacks by militants there last year crippled oil production. Yar'Adua had tried to peacefully end the insurgency but those efforts frayed due to his increasing illness.

Jonathan said Yar'Adua left a "profound legacy" for him to follow.

"He was not just a boss, but a good friend and a brother," Jonathan said.

Some Nigerians who awoke to the news of Yar'Adua's death were initially skeptical, as the masses remained uncertain about the ailing leader's condition for months.

Yet the streets in Lagos, the country's sprawling megacity in the south, remained quiet as Jonathan declared a public holiday and the start of a weeklong mourning period. Security agents remained tense, however, and a member of the State Security Service, Nigeria's secret police, stopped an Associated Press reporter from conducting interviews with passers-by.

Analysts said Nigeria's future will depend largely on what happens in the coming weeks and months.

"It now revolves around what the informal power-sharing between the north and the south, the Christians and the Muslims, is actually going to work out," said John Campbell, a former U.S. ambassador to Nigeria who now is a fellow at the Council on Foreign Relations. "One chapter is finished, another chapter is starting."


Associated Press Writers Bashir Adigun in Abuja, Nigeria and Lekan Oyekanmi in Katsina, Nigeria contributed to this report.