Lubumbashi - The Democratic Republic of Congo's top opposition candidate for the upcoming presidential election flew to South Africa for medical treatment on Friday, one day after authorities issued an arrest warrant for him on charges his supporters say are politically motivated.Moise Katumbi's lawyer, Georges Kapiamba, told The Associated Press late on Friday that his client had boarded a flight that would take him from Lubumbashi to South Africa "for appropriate care".The move postpones the prospect of his arrest, although the authorities who granted him permission to fly insisted he must return to face the charges of hiring mercenaries.It was not immediately known what medical ailment Katumbi had, although he was hospitalised in Lubumbashi on Thursday at the time his arrest warrant was announced on state television."He boarded the plane himself, but he is weak," Kapiamba said.Prosecutor Flory Kabange Numbi said Katumbi would be allowed to travel, but warned he is required to return to Congo to face the charges in the ongoing criminal case.A breach of this condition "would lead me to withdraw the authorisation", he wrote.It remains unclear what power authorities in DRC would have to compel Katumbi to return, though any prolonged absence could complicate his bid for the presidency.Longtime incumbent Joseph Kabila is constitutionally barred from seeking another term, but some fear he may try to stay in power by delaying the elections. He has yet to comment publicly on his intentions despite the controversy over his political future.Back in March, government authorities brought four of Katumbi's bodyguards, including one American, to the capital of Kinshasa and accused them of being mercenaries.Kabila took office in 2001 after the assassination of his father. A court recently ruled that he could stay in power beyond December if the elections were delayed so as to ensure a head of state remains.The DRC, an enormous country with vast mineral resources, was beset by decades of dictatorship and then back-to-back civil wars after its independence from Belgium. Scores of militia groups and rebels continue to destabilise the country's east more than two decades after the end of the Rwandan genocide, when many of those who carried out the killings fled across the border into eastern Congo.