Burundi's interior minister on Sunday denied government involvement in an alleged attempt by a policeman to assassinate a prominent opposition leader.

An armed plainclothes policeman was arrested on Saturday after being spotted acting suspiciously near a bar in the capital Bujumbura where Charles Nditije, a leader of an opposition faction of the Uprona party, was meeting aides.

Nditije said the man was wrestled to the ground by his bodyguards and had admitted to "being on a mission to assassinate me, without saying who had sent him". He also said it was "no coincidence" that the incident occurred the day before he was scheduled to hold a party meeting that "the interior ministry wants to prevent at all costs".

"This is shameful for Burundi, because nowadays opponents are imprisoned, exiled or assassinated," he added.

But Interior Minister Edouard Nduwimana moved to allay suspicions of a state connection to the incident. "It would be deplorable if there was an attempt to assassinate Charles Nditije, because this is outdated conduct whether for political motives or something else," the minister said.

"But it would be even more deplorable if it was orchestrated by himself, so we have to allow the relevant services to first shed some light on the case," he added.

A police source meanwhile insisted the incident appeared to be the result of a misunderstanding, saying the alleged would-be assassin — who works as a special protection unit of the force — was drunk and was attacked by a "nervous and paranoid" Nditije and his aides.

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The incident comes amid mounting political tensions and a rise in reports of political violence in Burundi in the run-up to next year's elections, when President Pierre Nkurunziza is expected to seek a third term that opponents say is unconstitutional.

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Uprona, Burundi's main Tutsi party, pulled out of the governing coalition led by Nkurunziza's Hutu-majority CNDD-FDD party earlier this year. The pullout upset a delicate power-sharing arrangement between Burundi's majority Hutu and minority Tutsi communities, who are still struggling to reconcile after decades of conflict.

The ruling CNDD-FDD party had been accused of forcing out Nditije as Uprona party chairman and replacing him with a sympathiser. The party is now officially led by a pro-government figure put in place by the interior ministry, but Nditije has been challenging the change in leadership.

On Sunday, riot police prevented Nditije and hundreds of supporters from entering Uprona's headquarters. The group then briefly demonstrated in surrounding streets, but no violence was repo