Nigeria says President Goodluck Jonathan has fallen ill in London and has been "advised to rest for a few days."
A statement from the presidency says Mr. Jonathan was due to attend an investment conference in the British capital Thursday but was unable to attend.
The statement says the president's condition is "nothing serious" and that the medical attention he sought was only a precaution.
Mr. Jonathan turned 56 this week.
He has been Nigeria's president since 2010. The country is Africa's most populous and the continent's biggest oil producer.