DR Congo's justice minister said on Wednesday he had ordered a probe into the alleged use of foreign mercenaries by opposition politician Moise Katumbi, who later announced his candidacy for president.
Katumbi hit back at the mercenary allegations describing as a "grotesque lie" claims his camp were recruiting mercenaries specialised in "training and the use of weapons, as security guards or bodyguards".
"It's a disgrace, a grotesque lie... they are simply looking to harm me.... Never will I, Moise Katumbi, take up arms for power," he told AFP, adding that his "struggle is democratic and peaceful out of respect for the constitution".
Justice minister Alexis Thambwe Mwamba earlier told journalists he had given orders to the general prosecutor to open a judicial case in the southeastern former province of Katanga.
"We have documented proof that several former American soldiers are currently in Katanga in the service of Mr Katumbi," he said, adding that the mercenaries were being recruited via a "network with a company based in Virginia in the United States".
On April 24, four members of Katumbi's entourage including an American were arrested in DR Congo's second city Lubumbashi, the capital of Katanga, and transferred to Kinshasa.
Thambwe accused American "ex-corporal Lewis Darryl of having tried to force a police barrier during an opposition protest" in Lubumbashi on Friday and "having tried to flee during his transfer from Ndjili airport to Kinshasa".
The minister said seven other former American soldiers and at least two South Africans had been staying in residences belonging to Katumbi, "for reasons that the inquiry will clarify".
Katumbi was formerly governor of Katanga, which has since been split into several different administrative regions.
He joined the opposition in September after quitting as governor and leaving the party of President Joseph Kabila.
Popular and charismatic, the 51-year-old wealthy businessman is also head of the prestigious Tout-Puissant Mazembe football club, three-time winner of the African Champions League.
A coalition of opponents of Kabila announced Sunday that they had chosen Katumbi as their candidate to run against Kabila in the presidential election.
On Wednesday Katumbi wrote on Twitter: "I accept this heavy responsibility with humility."
On Friday the politician accused the regime of targeting him with "false allegations", drawing reference to the "supposed recruitment of foreign mercenaries in Katanga province" and a report, by a TV station close to the government, of "the existence of training camps".
Authorities are under pressure from the international community to hold the polls as planned in November before Kabila's second — and constitutionally last — mandate ends, but this appears increasingly unlikely.
DR Congo's political climate has grown increasingly tense, with Kabila's opponents accusing him of seeking to extend his stay in power.
The country has been in crisis since Kabila's re-election in late 2011 in polls marred by irregularities and massive fraud.
Kabila assumed power after his father, president Laurent Kabila, was assassinated in 2001.