The national executive committee of Nigeria's ruling party has endorsed President Muhammadu Buhari to seek a second term in an election next year, two senior party sources told Reuters on Wednesday.

Buhari, who took office in May 2015, has not yet said whether he intends to seek re-election. The 75-year-old leader spent five months on medical leave in Britain last year for an unspecified ailment, raising questions about his ability to run Africa's most populous nation.

The national executive committee of the president's All Progressives Congress (APC) party, which takes decisions on the party's direction, held a one-day meeting which concluded late on Tuesday.

"The party made it clear that this endorsement is not an automatic ticket for the president," one of the sources said, adding that the party would still conduct a presidential primary to be fair to other potential candidates.

A spokesman for the president could not immediately be reached for comment.

Nigeria's political parties must select their candidates for the 2019 presidential election between August 18 and October 7 this year. Presidential and parliamentary elections are scheduled to take place on February 16, 2019.

Adebayo Shittu, Nigeria's minister of communications who played a prominent role in Buhari's 2015 campaign, said in January he would chair a group to support the re-election of Buhari and Vice President Yemi Osinbajo.

Campaigning for the re-election of a president in Nigeria has often started with such support groups before the incumbent declares his intention to run again.