Burundi police on Wednesday clashed with supporters of an ex-rebel chief who now heads the main opposition, wounding about 10 people, local media reported, while an activist said one victim died.

The police deployment outside the ex-rebel chief's home came as tensions mount ahead of presidential elections on June 28, with a number of grenade attacks having also occurred since the weekend, wounding about 15.

"Police intervened this afternoon at Agathon Rwasa's home," said Pierre Claver Mbonimpa, head of the Association for the Protection of Detained Persons and Human Rights.

"They used tear gas, fired live rounds and wounded about 15 seriously, including one who died from his injuries."

He said about 40 people were arrested and claimed officers also used rocket launchers, with one rocket landing on Rwasa's house, which is located in the hills overlooking the capital.

Mbonimpa denounced police for what he called excessive violence, but the authorities disputed his account.

A radio and television station reported about 10 wounded.

Police spokesman Pierre Chanel Ntarabaganyi said officers did not open fire, saying one person was lightly injured in a scramble that occurred after authorities showed up. "Police did not use rockets and they did not shoot," he said, adding 32 people were detained.

Officials from the National Liberation Forces, which Rwasa heads, could not be reached for comment and police blocked access to the leader's home.

The police spokesman said a false rumour that Rwasa would be arrested had led to his supporters gathering around his home to prevent it from happening.

According to Ntarabaganyi, Rwasa's supporters then began to search vehicles and those who passed in the area. "Police could not tolerate that and had to intervene," he said.

Opposition parties rejected the results of May 24 local elections, claiming fraud, and have decided to boycott the June 28 presidential poll, leaving President Pierre Nkurunziza as the only candidate.