Troops from Niger and Chad killed 47 Boko Haram fighters when they repelled an attack by the Islamist insurgents in southeastern Niger, Chad's army said on Tuesday. 

The fighting took place in Bosso, a Niger village near the border with Nigeria.

Nigeria's main opposition on Tuesday claimed victory in the country's tense general election as former military ruler Muhammadu Buhari pulled ahead of President Goodluck Jonathan in the vote count.

If confirmed, it would be the first democratic change of power in the history of Africa's most populous country.

Nigeria's President Goodluck Jonathan and his ruling Peoples Democratic Party (PDP) were marginally ahead of his main challenger, as the first general election results came in on Monday.

Jonathan and the PDP polled 2,322,734 votes overall against 2,302,978 for former military ruler Muhammadu Buhari, of the All Progressives Congress (APC) -- a difference of 19,756.

U.S. Secretary of State John Kerry and his British counterpart Philip Hammond Monday voiced fears over possible political interference in Nigeria's vote count, as the country awaited the results of weekend elections.

"We have seen no evidence of systemic manipulation of the process. But there are disturbing indications that the collation process -- where the votes are finally counted -- may be subject to deliberate political interference," the two diplomats said in a joint statement.

Nigerians on Monday awaited the first results of a closely fought general election, with protests over the conduct of the vote and a warning of manipulation of the count heightening fears of poll-related violence.

The presidential election pitting President Goodluck Jonathan against former military ruler Muhammadu Buhari is the closest in Nigeria's history, and first with a credible opposition challenge.

U.N. Secretary General Ban Ki-moon on Sunday congratulated Nigerians for holding "largely peaceful and orderly" elections despite Boko Haram attacks and urged them to continue to maintain a peaceful atmosphere.

Ban condemned attacks carried out by "Boko Haram and others who have attempted to disrupt" the presidential and parliamentary polls.

Nigerian troops battled scores of Boko Haram fighters outside the northeastern city of Bauchi on Sunday, residents and a military source told AFP.

Soldiers supported by two fighter jets intercepted the militants who were in 20 pick-up trucks at Dungulbe village, seven kilometers (four miles) from the city, and engaged them in fierce fighting.

Nigeria's closely fought general elections were forced into a second day on Sunday after failures in controversial new technology snarled the polling, including for President Goodluck Jonathan.

Authorities reopened some 300 polling stations -- of a total 150,000 -- where devices to read biometric voter identity cards did not work properly on Saturday.

Problems with new technology on Saturday forced a 24-hour extension to the presidential election in Africa's most populous nation, Nigeria, and renewed Boko Haram violence hit the knife-edge vote.

The Islamist militants were suspected of killing seven in separate attacks in northeastern Gombe state, including at polling stations, while on Friday, 23 people were beheaded in Borno.

U.N. Secretary General Ban Ki-moon on Friday called for transparent and peaceful elections in Nigeria on the eve of the vote that will be closely-watched by world governments.

"The international community has high expectations that Nigeria will provide leadership in setting a high standard for this election," Ban said in a statement.