Story highlights Incumbent President Goodluck Jonathan acknowledges defeat, says he delivered on promise of fair elections

Muhammadu Buhari's party says Jonathan called to concede even before final results are announced

Buhari is a 72-year-old retired major general who ruled in Nigeria in the 1980s

(CNN) Incumbent Goodluck Jonathan phoned former military leader Muhammadu Buhari on Tuesday to concede defeat in Nigeria's presidential elections, Buhari's party says.

Jonathan acknowledged the phone call and his defeat in a written statement to his countrymen.

"I thank all Nigerians once again for the great opportunity I was given to lead this country and assure you that I will continue to do my best at the helm of national affairs until the end of my tenure," he said.

The Independent National Electoral Commission is still announcing the final tally in the polls, but early numbers indicate Buhari, now the President-elect, has an overwhelming majority of votes.

Buhari ruled Nigeria from late 1983 until August 1985 after ousting his predecessor in a coup.