At full tally of the votes won in the 21 February presidential election in Niger, incumbent President Mahamadou Issoufou won 48.4 percent of the vote, falling short of an outright majority.
A run-off will now be conducted between him and jailed opposition leader Hama Amadou, according to provisional results on Friday.
Amadou, a former prime minister who came second with 17.8 percent, has been in prison since November on charges relating to a baby-trafficking scandal. He says he is innocent and a victim of political repression.
A coalition of four parties agreed before the election to back the candidate that came second in a bid to defeat Issoufou. Those parties gained a cumulative vote of around 38 percent.
Issoufou is bidding for a second term and has vowed to tackle poverty and improve security in the West African country that is one of the poorest in the world.
Niger also faces a threat from Nigeria-based Islamist militant group Boko Haram, which has staged a series of cross-border attacks in the southeastern Diffa region, forcing the government to impose a state of emergency there.
Turnout in the election was nearly 67 percent, according to the National Electoral Commission.