PARIS, Sept 17 (Reuters) – United Nations Secretary-General Antonio Guterres has expressed “extremely concerned” about Burundi’s new president Moustapha Kanyore’s political rise and warned of the dangers of an armed coup, a U.N. spokeswoman said on Sunday.

The 36-year-old appeared with government officials in a crowd of supporters singing and dancing as he was elected president on Saturday at an election congress.

“There was intense fire from a grenade belt (inside the auditorium) but no casualties among the members of the assembled gathering and of the security forces, including military, police, intelligence agents,” the spokeswoman said.

“There were many accusations of vote-rigging, such as lack of ballots, absence of ballots, absence of ballots being secured,” she said.

“There is no way of knowing how credible the result really was,” she said.

France, Burundi’s only permanent U.N. Security Council member, strongly condemned the vote.

“The election of the new president in Burundi was marred by political fraud,” Foreign Minister Jean-Yves Le Drian said in a statement on Saturday.

There was no immediate reaction from Rwanda, which has a small but active U.N. peacekeeping mission in Burundi, where the U.N. peacekeeping mission is based.

France and Rwanda have both fired peacekeepers after years of violence in the central African nation, in which hundreds of people have been killed. (Reporting by Matthias Blamont and Robert Woodward; Editing by Andrew Heavens)