The government in Kinshasa meanwhile told people to expect an important announcement regarding the appointment of a prime minister by Kabila's successor, Felix Tshisekedi.

Katumbi, 54, a wealthy businessman of mixed Greek and Congolese origin, served as the elected governor of Katanga in southeastern DR Congo before the province was divided up in a territorial revision.

He was once an ally of Kabila but the pair fell out. Katumbi was given a three-year jail term in absentia for alleged property fraud -- an accusation he denied -- and was barred from standing in last December's elections.

The conviction was annulled before Katumbi flew back to his homeland three years to the day after he left for Belgium, onetime colonial power in the vast central African country.

"The truth always triumphs in the end," Katumbi, the owner and president of the renowned TP ("All Powerful") Mazemba football club, told his fans at the airport.

"I return for peace and for national reconstruction in our country," he said.

Katumbi returned in a private jet to find supporters, many dressed in white, lining the road between the airport and the centre of Lubumbashi, now the capital of mineral-rich Haut-Katanga province.

He has also been an opponent of Tshisekedi, who took power after the disputed poll. Kabila stepped down after 18 years in office that began when his father was assassinated while warfare ravaged the country.

'Daybreak always comes'

Katumbi has yet to make clear what role he plans to play. In the election, he backed Martin Fayulu, another wealthy businessman who claims that he was the true winner of the December 30 ballot.

In a tweet, Fayulu said, "It doesn't matter how long night lasts, daybreak always comes. Welcome home to @MoiseKatumbi."

Meanwhile, Tshisekedi's spokesman said an important announcement would be made on national radio and television.

The current prime minister Bruno Tshibala "has turned in his resignation", according to the Top Congo radio station, heralding "the imminent announcement of a successor".

Also on Monday, the World Health Organization urged different political factions in DR Congo to unite in the battle against Ebola, warning that the risk of spread "remains very high".

"Ebola does not take sides. It is the enemy of everybody," WHO Director-General Tedros Adhanom Ghebreyesus told the opening of the organisation's annual assembly in Geneva.

Nearly 1,200 people have lost their lives since last August in the 10th outbreak of the disease in the country where it was first identified in 1976.

The bid to cope with the outbreak is hampered by the serious unrest affecting parts of the country, including attacks on medical teams as well as fighting.

Political clout

Sworn in on January 24, Tshisekedi has struggled to push ahead with his declared programme of reform. His choice of prime minister is expected to be acceptable to Kabila, who amassed extensive political clout after 18 years in power.

Kabila's political allies retain the upper hand in parliament, provincial assemblies across the vast and unstable country and the posts of governors. His men also play a major role in security services.

Katumbi's return coincided with a visit by French Foreign Minister Jean-Yves Le Drian to Kinshasa, where he went into talks with Tshisekedi as the highest ranking European official to do so since the election.

"The election finally finished in a kind of African-style compromise," Le Drian said in the wake of the vote, after challenging the official outcome.

On Monday, the French minister pledged "a programme of 300 million euros for the duration of Mr Tshisekedi's mandate" in sectors including development, training, health, security, agriculture and energy.

He welcomed "the fact of opening up democratic procedures, ... the fact of welcoming opposition figures, the fact moreover of finding the way to Europe again."