Niger's president is running for a second term against an opponent who had to campaign from behind bars before being flown last week to Paris for medical treatment.

President Mahamadou Issoufou finished first in the first round of balloting last month but without the outright majority he needed to avoid a second round.

The second-place finisher, Hama Amadou, earned nearly 18 percent of the vote despite having been detained since November for alleged involvement in a baby-trafficking scheme, a charge he has dismissed as politically motivated.

Amadou was transferred to a hospital in Niger's capital, Niamey, on March 11 before being flown to Paris last week. His spokesman has not given details on his health condition. An opposition coalition has said it will not recognize the results of Sunday's runoff.