ABUJA, Feb 26 — Muhammadu Buhari today extended his lead in Nigeria's presidential election as more results were announced amid opposition charges of a rigged outcome.

The 76-year-old incumbent, who is seeking a second term of office, won Niger state in the north-central region as well as Jigawa and Kaduna in the key northwest battleground.

That took his tally so far to 10 states. His main challenger, former vice president Atiku Abubakar, has won four states and the Federal Capital Territory of Abuja (FCT).

To win, a candidate needs a majority of votes and at least 25 percent of support in two-thirds of Nigeria's 36 states and the FCT.

Buhari, a former military ruler, has a total of 5,377,275 votes versus Abubakar's 3,848,175.

The chairman of the Independent National Electoral Commission (INEC), Mahmood Yakubu, said he expected "very substantial progress" in announcing results today.

"Our intention is to conclude this process speedily and we are determined to do so," he said, after complaints about the length of time to declare results.

Voting was held on Saturday, a week after the electoral commission postponed the election because of logistical difficulties in the delivery of ballot boxes and materials.

Buhari's ruling All Progressives Congress (APC) and Abubakar's Peoples Democratic Party (PDP) have accused each other of conspiring with INEC to rig the result.

Neither has presented evidence, although election observers have reported instances of vote-buying, intimidation and violence towards voters and officials on election day.

Several international monitoring bodies warned that repeated postponements could undermine confidence in the electoral process, after similar delays in 2011 and 2015.

A total of 72.7 million people were eligible to vote in the presidential poll as well as parliamentary elections held at the same time. — AFP