NIAMEY (Reuters) - An opposition coalition in Niger says it will boycott a run-off election on Sunday it says is tainted by fraud and called on its supporters not to vote, paving the way for President Mahamadou Issoufou to win a second term.

The coalition of parties supporting Mahamadou called the boycott “absurd” and urged all Nigeriens to go out and vote.

Issoufou, a Western security ally in West Africa, won the first round comfortably last month with 48 percent of votes but did not clinch the majority required to win in a single round.

His main opponent Hama Amadou, who came in second with 18 percent of the vote, was jailed in November in connection with a baby-trafficking scandal.

Hama, who says he is innocent and a victim of political repression, was flown out of the country earlier this week for health treatment, a government spokesman said.

The Coalition for an Alternative (COPA), which unites about 20 political parties including Amadou’s MODEN, says the constitutional court did not follow procedure when it announced the first-round results and had not proven its independence.

“COPA reiterates its boycott of elections by inviting its members and supporters not to come out on March 20, to stay at home in order to devote the day to prayer and contemplation,” COPA said.