DR Congo's justice minister on Wednesday said he had ordered an investigation into the alleged use of foreign mercenaries by opposition politician Moise Katumbi, a likely contender in presidential elections due this year.

"I gave the orders to the PGR (General Prosecutor of the Republic) to open a judicial case in the former province of Katanga," justice minister Alexis Thambwe Mwamba told journalists in Kinshasa.

"We have documented proof that several former American soldiers are currently in Katanga in the service of Mr. Katumbi."