US intelligence reports claim France has been behind a covert military operation to prop up President Mobutu as Mr Kabila's rebel forces advance across Zaire.
The operation, which began within weeks of the outbreak of the rebellion, involved obtaining three combat aircraft from Yugoslavia for Mr Mobutu's forces, along with pilots and mechanics and the services of least 80 mercenaries in early January, the reports claim.
Most of the mercenaries were to have been Serbs; others were Belgians and French.
A US official said it could not be determined whether the operation was continuing, but that the planes and crews were still in Zaire.
A few weeks ago, Zairean government forces received five MiG 21s, which a senior Western diplomat thought were from Yugoslavia, though he said he did not know who had paid for them.
A spokesman for the French Foreign Ministry, Mr Jacques Rummelhardt, denied that Paris was involved in any covert operation, or had connections with Geolink, a company the intelligence reports have cited as part of the alleged plot.
Details of the operation are murky and Western diplomats said it was quite possible that the French intelligence service might have been running such activities without other branches of the government knowing about it.
A US official said that at one point Mr Mobutu began negotiating with Executive Outcomes, a South African company that provides mercenaries, but the company wanted $100 million, which he could not afford.
"Our suspicion is that the French stepped in and said `We'll do it. You don't need Executive Outcomes'," said the official.