Nigerien President Mahamadou Issoufou has taken a clear lead in the presidential election but falls short of an outright majority, forcing a runoff against jailed opposition leader Hama Amadou, official results say.

Niger's Independent National Electoral Commission, CENI, said on Friday that Issoufou, 63, won 48.41 percent of the February 21 vote and his nearest rival, Amadou, got 17.41 percent.

The electoral commission said the turnout in the election was nearly 67 percent.

Issoufou, who is bidding for a second term and has promised to tackle poverty and improve security in the West African country, failed to score the majority "knock-out" victory he had pledged.

Amadou, a former premier, has been in prison since November on charges related to a baby-trafficking scandal. He says he is innocent and a victim of political repression.

The final round is due to be held before the end of March.

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.

The African Union, which deployed 40 observers, has said it was generally satisfied with the organization of the vote, despite delays in some areas caused by logistical glitches.

But the opposition COPA 2016 coalition has said it "reserved the right to reject the grotesque and cooked up results."

Prior to the poll, the opposition had anticipated a run-off vote, vowing there would be no easy victory for incumbent Issoufou.

Despite an abundance of uranium, coal and oil, Niger is one of the poorest countries in the world.

A total of 7.5 million people were eligible to vote across the country on the edge of the Sahara desert, where security is a growing concern after attacks by militants from neighboring Nigeria, Mali and Libya.