ABUJA, Nigeria (AP) – The ruling party candidate was declared the winner Monday of Nigeria’s presidential elections, following a vote that international observers said was marred by widespread problems including ballot box stuffing and phony results in Africa’s largest oil producer.

The runner up rejected what he called the “the most blatantly rigged election results ever produced in Nigeria.”

As was widely expected, Umaru Yar’Adua, the 56-year old governor of northern Katsina state, won in a landslide. Elected vice president was Goodluck Jonathan, a governor from an oil-rich southern state.

The America-based International Republican Institute and the European Union identified numerous voting-day irregularities and said the election failed to meet international standards.

In Washington, State Department spokesman Sean McCormack said: “Based on the reports that we have seen, these were flawed elections and in some cases deeply flawed elections.”

Turnout appeared low for Saturday’s vote to replace President Olusegun Obasanjo, who leaves office May 29 in Nigeria’s first transfer of power between elected, civilian leaders.

In a nationwide address ahead of Monday’s announcement, Mr. Obasanjo accused the opposition of “fanning the embers of hate” and engaging in “outright subversive activities.”

Electoral commission Chairman Maurice Iwu said Yar’Adua won about 24.6 million votes, more than three times the number garnered by the runner up, General Muhammadu Buhari. Some 61 million Nigerians registered to vote. Iwu gave no turnout figures.

Mr. Obasanjo admitted that the vote was flawed, but said Nigerians were nonetheless devoted to democracy. He said losers should redress grievances through the courts.

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

Oil prices rose Monday as traders worried about the political mood in Nigeria. 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.

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

“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,” said Max Van den Berg, head of the EU observer mission.

Nigeria’s other elections 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.

A Nigerian observer mission called Sunday for the vote to be reheld.

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.” Mr. Buhari called the vote “the most blatantly rigged election results ever produced in Nigeria,” and said: “I completely and wholeheartedly reject these results as a sham.” He did not call for public protests.

Mr. Obasanjo, also 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. He was prevented from running again by constitutional term limits.