As counting of votes continues in Nigeria, President Muhammadu Buhari has taken an early lead in the election results, amid allegations of manipulation by the main opposition.

Eleven of 36 states have been announced, with the process resuming at 10 am and expecting to continue late into the day or even Wednesday. States with the largest numbers of voters have yet to be announced.

According to the provisional results, Buhari has won in seven states, while his competitor Abubakar Atiku took four states. However, in the 11 states and the Federal Capital Territory, Buhari defeated Atiku by 290,105 votes, an indication of the hot contest. Abuja, Nigeria's capital, is located in the Capital Territory.

Buhari leads in Ekiti, Gombe, Kogi, Kwara, Nasarawa, Osun and Yobe states, while Atiku leads in Abia, Enugu, and Ondo states as well as in the Capital Territory.

Following the announcement of the provisional presidential results, Atiku's People's Democratic Party, or PDP, alleged that there had been irregularities in the vote.

In a news conference, party chairman Uche Secondus said the results had been inflated in favor of the ruling All Progressives Congress.

Secondus alleged that the Congress, together with the state security agents, was working with the Independent National Electoral Commission, or INEC, to manipulate the vote.

"The results are incorrect and unacceptable to our party," Secondus said. He claimed that Congress officials, working with election commission, altered results. "This must be resisted. INEC must live up to its responsibility. They are under pressure. We have the facts and when the time comes, we will begin to release them," Secondus said.

In an interview with Al Jazeera, a Congress leader dismissed the allegations by the PDP. "It is antidemocratic and seeks to frustrate the sacrifice that Nigerians have made to vote and express their will," Babatunde Fashola, the Minister of Power, Works and Housing, told Al Jazeera.

Largely peaceful

The African Union Election Observation Mission, led by Hailemariam Desalegn Boshe, the former Ethiopian prime minister, assisted by Minata Samate Cessouma, the African Union Commissioner for Political affairs, observed that the Nigerian election process was largely peaceful, orderly and in conformity with the country's legal framework.

Nevertheless, the mission stated that certain parts of the country, particularly in the North East, South-South and Middle Belt regions, faced security challenges.

In the spirit of cooperation and solidarity, the mission urged the political parties and candidates to uphold the commitment to peaceful elections and resolution of disputes in keeping with the two peace accords signed in December and February.

They were also urged to call on their supporters to remain calm and peaceful and refrain from any action that might incite post-election violence.

"In case of any grievances over the election results, political parties and candidates are encouraged to use the legal instruments at their disposal to seek redress," a statement from the mission read.

The mission also urged the election commission to expeditiously and transparently collate and announce the results of the presidential and national assembly elections according to law.