The Democratic Republic of Congo has ordered an investigation into the alleged use of foreign mercenaries by the country's opposition leader and potential presidential candidate Moise Katumbi.

“I just gave the instruction to the general prosecutor of the republic to open a judicial case against the former governor of the province of Katanga, Moise Katumbi,” DR Congo’s Justice Minister Alexis Thambwe Mwamba said on Wednesday.

“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.”

The recruits were specialized in training and the use of weapons, as security guards or bodyguards, the minister noted.

The move came after four members of Katumbi's entourage including an American were arrested in Katanga on April 24, and transferred to the country’s capital, Kinshasa.

The justice 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, 51, was formerly the governor of Katanga, a DR Congo's southern province, and joined the opposition in September last year after quitting as governor and leaving the party of incumbent President Joseph Kabila.

The opposition leader, who has also announced his run in the country's November presidential election, adamantly dismissed the allegations leveled against him over the use of mercenaries.

“It's a disgrace, a grotesque lie... they are simply looking to harm me.... Never will I, Moise Katumbi, take up arms for power,” said Katumbi, adding that his “struggle is democratic and peaceful out of respect for the constitution.”

DR Congo has been struggling since President Joseph Kabila’s 2011 re-election, which is said to have been marked with voting irregularities. The country has been through two wars since Kabila came to power.

Political tensions are again high in the African country as new elections are due later this year.