The former governor of the mineral-rich southern province of Katanga, who has been living in self-imposed exile in Belgium since May 2016 after falling out with President Joseph Kabila, had intended to fly home on Friday.
But Lubara on Thursday announced that he could not allow him to return as planned to the southeastern city.
“I regret to inform you that I cannot agree to your request,” Lubara said, invoking “airspace and landing non authorization” and an “active judicial file” concerning Katumbi.
“Lubumbashi is a city of peace and would like to consolidate this achievement,” he added.
Earlier Thursday, aides to Katumbi met with United Nations officials to discuss his return, sources said.
He had filed flight plans to arrive in the provincial capital of Lubumbashi on Friday.
If he does return, however, he faces possible arrest after being handed a three-year jail term in absentia in June 2016 in a case of alleged property fraud. He has also been accused of hiring mercenaries and for possessing an Italian passport — Congolese law does not allow double nationality. He denies all charges.
A leader of Katumbi’s election party, Ensemble, said there was concern about “security risks” in the light of “events” that occurred on Wednesday, when former warlord Jean-Pierre Bemba returned to Kinshasa.
“There are risks of breakdowns which could put civilians and political figures such as Katumbi in danger,” said Delly Sesanga, Ensemble’s secretary general.
The UN peacekeeping mission to the Democratic Republic of Congo, MONUSCO, confirmed a meeting had taken place, in the context of its “good offices” in the DRC.
But MONUSCO’S spokeswoman, Florence Marchal, added that its “mission is not to ensure the protection of (individual) personalities”.
The Congolese NGO Association for Access to Justice (ACAJ) said in a statement that the minister of justice should “stop the political pressure” to “arbitrarily arrest” Katumbi.
Kabila’s 17-year rule has been criticised for rights abuses, corruption and incompetence.
He was scheduled to stand down at the end of 2016 after his second elected term, technically the last permitted under the constitution.
But he has stayed in office, invoking a constitutional clause enabling him to remain in power until a successor is elected.
He has refused to spell out whether he will seek a new term in the vote. The elections, twice postponed, are due to take place on December 23.
Dozens have died in anti-Kabila protests amid the mounting political uncertainty.
On Wednesday, former warlord and ex-vice president Bemba — another declared election contender — flew into Kinshasa to a triumphant welcome from tens of thousands of supporters.
The ex-rebel leader spent the last 11 years abroad, a decade of it behind bars.
He travelled to the electoral commission on Thursday to file his candidacy for the presidential election.
The International Criminal Court (ICC) in The Hague acquitted him of war-crimes charges in June.