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KANO, Nigeria — Nigeria's president was poised to win a second term in Africa's largest democracy, with unofficial results on Tuesday showing a victory, his campaign spokesman said — news that set off celebrations in the capital.

With President Muhammadu Buhari leading by nearly 3.5 million votes, it seemed his call for voters to give him another chance to tackle gaping corruption, widespread insecurity and an economy limping from a rare recession had resonated in the nation of 190 million people.

While many frustrated Nigerians had said they wanted to give someone new a chance, Buhari, a former military dictator, appeared to have retained enough support for victory in an oil-rich nation weary of a long string of politicians enriching themselves instead of the people.

Nigerian President Muhammadu Buhari speaks during a joint press conference with the German chancellor at the presidency in Abuja on Aug. 31, 2018 Pius Utomi Ekpei / AFP - Getty Images file

In a last-ditch effort to stop the official declaration of a winner, top opposition challenger Atiku Abubkar demanded a halt to the proceedings, claiming that data from smart card readers used in the vote had been manipulated. His party called for fresh elections in four states: Yobe, Zamfara, Nasarawa and Borno.

Buhari's party has rejected accusations of manipulation, and Fashola called on Abubakar, a billionaire former vice president who made sweeping campaign promises to "make Nigeria work again," to provide evidence backing his claims.

Abubakar, who hasn't made a public appearance since Saturday's election, should accept his loss gracefully and concede, Fashola added. "Let this nation move forward," he said.

As the state-by-state announcements of election results passed the halfway mark, Buhari was declared the winner in 15 of Nigeria's 36 states including its most populous ones, Lagos and Kano. Abubakar won 12, many in the largely Christian south, and the capital's territory.

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Final results weren't expected until early Wednesday in a race once described as too close to call. The president, who declared victory moments after voting in his hometown, told campaign workers Monday evening: "I congratulate you very much that you have succeeded."

The vote suffered from a surprise weeklong postponement and significant delays in the opening of polling stations. While election observers called the process generally peaceful, at least 53 people were killed, analysis unit SBM Intelligence said.

The death toll rose after an attack shortly before polls opened and claimed by the Islamic State West Africa Province extremist group in the northeast proved deadlier than first reported, with at least 17 people killed, head of research Cheta Nwanze told the AP on Tuesday.

It remains to be seen whether Abubakar will follow through on pledges to accept a loss, or challenge the results. A former U.S. ambassador to Nigeria, John Campbell, says the troubled election has given the candidates grounds to go to the courts. That route could take months.

In Kano, the heart of the country's Muslim north, there was relief that the sensitive region appeared to have avoided the deadly violence that occurred in other areas.

"Well, we thank God that at least we finished this safely, without any hitches," the state electoral commissioner, Riskuwa Shehu, told the AP minutes before carrying results to the capital.

Turnout appeared to be lower than expected, Shehu said, pointing to a number of factors, including the fear of possible violence after heated campaigning. The "disappointment" of a weeklong postponement likely also played a role, he said.

Nigerians' reactions to Buhari's apparent victory were mixed.

"Alhamdulillah," said 36-year-old Umar Ibrahim, using the Arabic phrase for "praise be to God" as he chatted with clients about politics at his tiny shop in Kano. "Up to now they say Buhari is leading, far. He is a good elder."

Grace Eje, a 25-year-old domestic worker, had held out hope for Abubakar, saying Nigeria needed someone new after Buhari. "No money, no work, no help from him," she said of the president, grimacing.

Many Nigerians have prayed for peace. They were surprised in 2015 when President Goodluck Jonathan conceded before official results were announced giving victory to Buhari, who pulled off the first defeat of an incumbent by the opposition in the country's history.

Some are worried that such a concession appears unlikely this time.

"Jonathan set the benchmark on how electoral outcomes should be handled," Chris Kwaja, a senior adviser to the United States Institute of Peace, a U.S. government-backed institution promoting conflict resolution worldwide, told the AP. "So far, it is unclear what the candidates will do."

For the presidency, a candidate must win a majority of overall votes as well as at least 25 percent of the vote in two-thirds of Nigeria's 36 states.

It was not yet clear how many of Nigeria's estimated 73 million eligible voters turned out. The YIAGA Africa project, which deployed more than 3,900 observers, estimated turnout at between 36 percent and 40 percent, down from 44 percent in 2015.

That would continue the trend of recent elections, even as many Nigerians were praised for their patience and resilience in this bumpy vote.