Muhammadu Buhari

His health has been a major cause of concern in a country where there are fears that a power vacuum could affect its recovery from recession.

In a brief message, the president said "there is no cause for worry".

Mr Buhari, 74, has left Vice-President Yemi Osinbajo in charge, just as he did when he left for London in January for seven weeks of medical leave.

Mr Osinbajo was widely praised at the time for his performance as acting president.

The President landed at the Kaduna Air Force base early Friday morning. His flight was diverted as the capital's airport is currently closed for repair work.

President Buhari flew to Abuja in a military jet and was received by the Vice President Yemi Osinbajo, who has been acting president in his absence.

Buhari also had a short meeting with his members of his Cabinet and announced to them that Vice President Osinbajo would continue to act as president, the AFP reports.

Buhari left the country on January 19 on what was supposed to be a 10-day holiday.

On a visit to Germany, he said: "I don't know which party my wife belongs to, but she belongs to my kitchen and my living room and the other room."

Mr Buhari was standing next to Chancellor Angela Merkel, who seemed to glare at him.

Aisha Buhari had said she might not back her husband at the next election unless he got a grip on his government.

Responding to questions by reporters, Mr Buhari said that having run for president three times and having succeeded at the fourth attempt, he could "claim superior knowledge over her".

Nigerian President Muhammadu Buhari pledged to end the insurgency by December 31. On Thursday he said his Government had "technically" defeated Boko Haram and reduced the group's capacity to mount "conventional" attacks in Africa's most populous nation.

But, in an expected show of defiance, Boko Haram countered with a series of devastating attacks on towns in the country's north-east, claiming dozens of fatalities in a bloody killing spree that began on Christmas Day.

The government is talking to Boko Haram members and it is trying to make sure they are genuine leaders, presidential spokesman Femi Adesina said in a tweet late Tuesday quoting President Muhammadu Buhari. Buhari is in France on a three-day state tour.

Military from Nigeria and Chad freed hundreds of hostages from Boko Haram captivity earlier this year but none of those rescued were from the 219 girls abducted in April 2014 from a school in Chibok.

Thursday's appointment comes as the West African nation's new president promised deeper collaboration with neighboring states in the fight against Islamic extremism.

President Muhammadu Buhari headed home Thursday after two days of talks in Yaounde, Cameroon, focused on Boko Haram.

Its attacks have spread across Nigeria's borders and forced tens of thousands of refugees to flee to neighboring states.

Buhari predicted in an interview with The Associated Press that Boko Haram would be defeated in 18 months or less.

But he conceded that Nigerian authorities lack intelligence about the girls still missing after the mass-kidnapping from the northern town of Chibok in April 2014 — an act that stirred international outrage and a campaign to "Bring Back Our Girls" that reached as far as the White House.