Spain's Foreign Ministry says Gabon's President Omar Bongo, one of the world's longest-serving leaders, is in a Barcelona hospital in stable but serious condition.
Officials and medical sources said Thursday that the 73-year-old Mr. Bongo is being treated at Barcelona's Quiron clinic.
The sources did not identify his ailment, but media reports say he is suffering from cancer.
Spanish Foreign Minister Miguel Angel Moratinos, touring the Balkans, told Spanish media that Mr. Bongo is "very sick."
On May 6, Mr. Bongo temporarily suspended his duties, saying he needed time to mourn the death of his wife, who died in March in a Moroccan hospital.
That same day, a French judge announced an investigation into whether Gabon's president and two other African leaders used embezzled funds to buy property, luxury cars and other goods in France.
Mr. Bongo has denied any wrongdoing.
He has ruled Gabon since 1967, and is Africa's longest-serving leader.
Gabon's constitution calls for Senate leader Rose Francine Rogombe to become caretaker president and organize a new presidential election in the event of Mr. Bongo's death.
Some information for this report was provided by AP and Reuters.