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LUBUMBASHI, Democratic Republic of Congo (Reuters) - Congo police fired teargas on Friday at thousands of supporters rallying outside the prosecutor’s office where a leading opposition presidential candidate was facing a hearing over accusations he was plotting a coup, a Reuters witness said.

It was the third time in five days that police have fired teargas at supporters of Moise Katumbi, the former governor of Congo’s copper-mining region, who the government accuses of hiring mercenaries as part of the plot against the republic.

Authorities in Democratic Republic of Congo have given scant details about the allegations made last week and which Katumbi denies.

Katumbi says the accusations are aimed at derailing his campaign to succeed President Joseph Kabila, who has ruled since 2001 but is barred from standing for a third term in an election set for November.

Police also threw rocks at the demonstrators, who flocked toward Katumbi when he arrived outside the prosecutor general’s office. One rock hit Katumbi’s older brother, Abraham, in the face.

“It’s sad that there is not a state of law - police officers who throw stones and wound my older brother,” Katumbi said before entering the building.

The hearing was just suspended after Katumbi said he felt unwell due to the teargas.

Dozens were killed in January 2015 in protests over a proposed revision of the electoral law that critics said was a ploy to keep Kabila in power beyond the end of his mandate. Kabila has not said whether he will leave power this year.