The cost of upgrading the Rafale to the standard required by the UAE, a potential buyer of 60 of France's most sophisticated combat aircraft, could reach 4-5 billion euros ($5.4-$6.7 billion), a report said.

"The client will at best pay only half (of the bill)," one source close to the talks told the French daily La Tribune.

France's Ministry of Defence and companies involved in the project -- Dassault Aviation, Thales and Safran -- would foot the rest of the bill.

The Ministry of Defence and Dassault Aviation could not be reached for comment.

France has so far failed to find a foreign buyer for the Rafale, which has both fighter and bomber roles, and has lost out to rivals offering cheaper, less high-tech models. – Reuters