Jailed Niger opposition leader Hama Amadou was flown to Paris for medical treatment on Wednesday, days before he is due to face a run-off election against President Mahamadou Issoufou.
Amadou, a former president of parliament, was jailed in November in connection with a baby-trafficking scandal but finished second to Issoufou in the first round of polling last month. The run-off vote is on Sunday.
“Amadou left Niamey on Wednesday afternoon for Paris in an air ambulance. One must know that the health ministry hired the plane,” said government spokesman Marou Amadou, who is also the minister of justice.
Opposition spokesman Ousseini Salatou said Amadou was earlier brought to the capital by helicopter from the town of Filingue, 180 km (110 miles) northeast of the capital Niamey, where he is being held in prison.
Amadou, who has not been convicted, denies the charges against him and says they are politically motivated. His supporters say he has been ill during his imprisonment. The nature of his illness was not immediately clear.
His doctor said on Monday he had lost consciousness once before being revived in the prison infirmary.
President Issoufou took office in April 2011, a year after a coup overthrew Tandja Mamadou.
He is working with Western nations to improve security in the Sahel region, where Islamist militants have carried out a string of recent attacks. Critics say Issoufou is becoming increasingly authoritarian and clamping down on dissent.