A plane carrying around 50 armed men has landed illegally in northern Central African Republic, the foreign minister has told the BBC.
Jean Paul Ngoupande said the plane had arrived from Sudan and was suspected of being linked to the rebellion in Chad.
Earlier this month, UN chief Kofi Annan said he was concerned that the fighting in Chad could further destabilise both Sudan's war-torn Darfur region and CAR.
Mr Ngoupande said he was lodging a complaint with the African Union.
Analysts say CAR is being used by Sudanese rebels as a crossing point to Chad.
Tension is rising in Chad ahead of elections due next week.
President Idriss Deby insists that the polls will go ahead despite a rebel attack on the capital N'Djamena earlier this month.
Sudan and Chad accuse each other of backing rebel groups.
Mr Ngoupande said his government was going to talk to the Sudanese authorities about the plane.
Earlier reports said that two planes had landed in CAR.
President Francois Bozize seized power in CAR three years ago, and since he stood successfully in a presidential election last year, a rebel movement has emerged in the north.
Thousands have fled the fighting, crossing into Chad.
But the BBC's Joseph Benamsse in the CAP capital, Bangui, says that military sources say CAR's rebel groups are no longer operating in the area where the plane landed.