The governing party candidate was declared the winner Monday after Nigeria's weekend presidential elections that were denounced by the opposition and declared deeply flawed by international observers.

As was widely expected, Electoral Commission Chairman Maurice Iwu said Umaru Yar'Adua, the 56-year old Muslim governor of northern Katsina state and candidate of departing President Olusegun Obasanjo's People's Democratic Party, won in a landslide.

"Umaru Musa Yar'Adua of PDP, having satisfied the requirement of the law and scored the highest number of votes, is hereby declared the winner and is duly elected," Iwu told reporters.

He said Yar'Adua won about 24.6 million votes, more than three times the number garnered by the runner up, Gen. Muhammadu Buhari, in Saturday's vote. Some 61 million Nigerians registered to vote. Iwu didn't give turnout figures.

Nigeria's main political parties have rejected the vote as fraudulent and international and local observer groups reported widespread irregularities. The European Union observer mission said Monday the vote wasn't credible, and the U.S. government called it flawed.

Asked on state television if he had expected to win, Yar'Adua's entourage broke into raucous laughter. The usually somber Yar'Adua, though, allowed only a tight smile and said: "I did because my party is strong. We enjoy the goodwill of Nigerians."

"I felt gratitude toward the almighty," said Yar'Adua, a Muslim. "I felt greatly humbled by the events of today and this mandate, greatly humbled."

In a nationwide address ahead of Monday's announcement, Obasanjo, who had been barred form running by term limits after two terms in power, accused the political opposition of "fanning the embers of hate" and engaging in "outright subversive activities."

Oil prices rose Monday as traders worried about the political mood in Nigeria, Africa's largest oil producer. Though the election was largely peaceful, traders said there were fears that the results could lead to further tensions.

A widespread violent reaction appeared unlikely, though. While Nigerians express frustration with the state of their democracy, their disillusionment and cynicism — and fear of the still-influential security forces — were likely to mute their response.

In his television address, Obasanjo acknowledged that the vote had been flawed, but said Nigerians were nonetheless devoted to democracy. He said any losers should redress any grievances through the courts.

One of the two main opposition parties has already said it would challenge the results in court.

Turnout appeared low for Saturday's presidential vote, which was marked by ballot-paper shortages in opposition strongholds, intimidation by thugs and open rigging favoring Obasanjo's party.

The electoral process, which included an April 14 vote for state offices and Saturday's vote for president and federal-level lawmakers, is meant to set up Nigeria's first handover of power between elected heads of state.

All other attempts since independence from Britain in 1960 have been overturned by coups d'etat or annulments. Dozens of Nigerians have died in civil strife related to the elections, and fraud was clearly visible on voting days.

On Sunday, a large, homegrown election observer mission called for the vote to be reheld, citing massive irregularities. The U.S.-based International Republican Institute said the voting failed to meet international standards, and citing ballot-box stuffing and phony results.

On Monday, the European Union monitoring group said the elections "have fallen far short of basic international and regional standards for democratic elections." Mission head Max Van den Berg. He cited widespread procedural irregularities, fraud during the counting process and violence.

"I am disappointed," he told reporters. "These elections have not lived up to the hopes and expectations of the Nigerian people and the process cannot be considered to have been credible."

In Washington Monday, State Department spokesman Sean McCormack said that he hoped the political parties involved would resolve any differences in the election through peaceful, constitutional means.

In announcing the outcome, Iwu said "the conduct of the 2007 elections has not gone without difficulties."

But he said distributing 65 million ballots in a country of 140 million people with poor road systems had been a massive logistical exercise. He said that the vote was held at all "show(s) the tremendous love God has for this country."

Iwu said Buhari, an 80's-era military ruler, had placed second with about 6.6 million votes. Vice President Atiku Abubakar, a former Obasanjo running mate who fell out with his boss, took 2.6 million ballots. He only rejoined the ballot last week after the Supreme Court ruled the electoral commission unlawfully disqualified him. The presidential ballots were reprinted last week in South Africa and the final papers only arrived in Nigeria the day before Saturday's vote.

If opposition party supporters heed their candidates' calls to reject the final outcome, it could undermine the ruling party's win, and potentially pit large segments of the population against each other.

Obasanjo, a former military ruler, won a 1999 election that ended 15 years of near-constant military rule. His 2003 re-election was marked by allegations of massive vote rigging.