NAIROBI, Kenya — Burundi’s top opposition leader went to the constitutional court Thursday to challenge the results of this month’s presidential election, alleging the vote was rigged in favor of the ruling party candidate.

“We’ve seen a lot of irregularities,” Agathon Rwasa told reporters. “There are many examples showing, for example, the stuffing of ballot boxes.” He said the electoral commission must be held accountable, adding that the electoral roll was never published.

“Not a single district, no single province was spared,” he said. “So the results proclaimed are fake.”

The court has eight days to decide. Rwasa said that if he is not satisfied he will take his argument to the East African Court of Justice based in Arusha, Tanzania.

On Monday the ruling party candidate, Evariste Ndayishimiye, was declared the winner of the May 20 election with 69 percent of the vote. Rwasa received 24 percent, according to the electoral commission. But a spokesman for his party said they believe Rwasa won with 57 percent.

Burundi’s Catholic bishops conference also has questioned the vote, saying this week they had witnessed “intimidation and constraints exerted by some administration officials who accompanied voters to the voting booths, the exclusion of observers from places where votes were counted, the intrusion of unauthorized persons into places where votes were counted, the stuffing of some ballot boxes” and voting in the name of the dead.

“The conference wonders if all these irregularities do not undermine the provisional results released by the electoral commission,” said Bishop Joachim Ntahondereye, the group’s president.

Ndayishimiye, 52, will succeed President Pierre Nkurunziza, who has been in power since 2005. The ruling party has said Nkurunziza will have the title “Supreme Guide” after he steps down, and many believe he will wield considerable influence behind the scenes. Ndayishimiye is expected to be inaugurated in August.

This election has not seen the widespread demonstrations and deadly violence that marked the previous vote in 2015 after Nkurunziza decided to run for a third term that many called unconstitutional.

The deadly turmoil badly damaged global relations, and Burundi became the first country to leave the International Criminal Court after it started investigating allegations of abuses.

The U.N. human rights office reported more than 300 extrajudicial killings and was kicked out of the country. Burundi’s government has denied allegations it targets its people, but Rwasa and his party reported harassment of party supporters ahead of this month’s vote.

The 56-year-old Nkurunziza surprised many in Burundi by deciding not to run again.