A Nigerian official says Vice President Goodluck Jonathan will continue leading the country while President Umaru Yar'Adua recovers from a long illness.
Presidential spokesman Olusegun Adeniyi made the announcement Wednesday, after Mr. Yar'Adua returned to the country from three months in a Saudi hospital.
In a statement, Adeniyi said the president's health has "greatly improved." But, he added, Mr. Jonathan will continue to oversee affairs of state until Mr. Yar'Adua "completes his recuperation."
An ambulance met the president's plane on the tarmac when it landed in Abuja early Wednesday.
There was no immediate sighting of the president, who has made no public appearances since flying to Saudi Arabia November 23.
Earlier this month, parliament made Mr. Jonathan the country's acting leader in the president's absence.
In a statement Wednesday, the United States said it hopes Mr. Yar'Adua's return is not an effort by his senior advisers "to upset Nigeria's stability and to create renewed uncertainty in the democratic process."
Nigeria is scheduled to hold a presidential election next year.
The president's prolonged absence sparked controversy over who was running the Nigerian government. Nigeria is Africa's most populous country and a major oil producer.
Mr. Yar'Adua remained officially in charge until lawmakers voted to make Mr. Jonathan acting president earlier this month. However, some lawyers and lawmakers have said that move was unconstitutional.
Since President Yar'Adua was hospitalized, officials have released little information about his health. He was originally reported to be suffering acute pericarditis, a dangerous inflammation of the membrane that covers the heart.
The 58-year-old president also has a chronic kidney ailment that required several previous trips abroad for treatment.
Some information for this report was provided by AP and Reuters.