KINSHASA (Reuters) - Democratic Republic of Congo’s top court on Monday definitively excluded opposition leader Jean-Pierre Bemba from December’s presidential election because of a witness tampering conviction at the International Criminal Court.

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Bemba, a popular former vice president, was tipped as one of the leading candidates to replace outgoing President Joseph Kabila. His exclusion from the race could spark a violent reaction by his supporters.

His defeat to Kabila in the 2006 election touched off deadly clashes in the capital Kinshasa between his supporters and state troops. He then spent a decade in prison in The Hague before his war crimes convictions for murders and rapes committed by his militia in Central African Republic were quashed in May.

In a judgment broadcast on national television, the constitutional court said the election commission had rightly invalidated Bemba’s candidacy last month, finding that witness tampering is a form of corruption as stipulated in the electoral law.

The Dec. 23 election is due to usher in Congo’s first democratic transition of power after Kabila agreed last month to respect constitutional term limits and step aside in favor of close loyalist Emmanuel Ramazani Shadary’s candidacy.

That announcement has calmed tensions that exploded into deadly street protests when Kabila refused to step aside at the end of his constitutional mandate in December 2016.

But fears persist of further violence with Kabila’s opponents accusing him of trying to rig the vote to ensure Ramazani’s victory.

“Congo has fallen very low!” the secretary-general of Bemba’s MLC party wrote on Twitter after the judgment.

Kabila’s camp denies that it is improperly trying to influence the election.

Besides Bemba, opposition leader Moise Katumbi was barred from re-entering Congo last month to register his candidacy after two years in exile.

Katumbi placed joint first in a rare public opinion poll in July with 19 percent of the vote. Another opposition leader, Felix Tshisekedi, also received 19 percent, while Bemba placed third with 17 percent.

Ramazani did not receive enough votes to be included in the results.

The constitutional court also on Monday upheld the invalidation of former prime minister Adolphe Muzito’s candidacy but reinstated another former prime minister Samy Badibanga as a candidate.