The French authorities have blocked the official aircraft of Ivory Coast's incumbent president, Laurent Gbagbo, at the Swiss-French airport at Basel.
The French foreign ministry confirmed on Sunday that the action had been taken at the request of the "legitimate authorities" of Ivory Coast, referring to Gbagbo's challenger, Alassane Ouattara.
The aircraft is being prevented from flying back to the west African state from EuroAirport, which is jointly operated by Switzerland and France.
Gbagbo has refused to recognise the results of November's presidential election which was won by Ouattara - a victory recognised by the international community, including the United Nations.
Thousands of civilians have been fleeing the country since and West African leaders threatened a military intervention on December 24 if Gbagbo did not hand over power.
It was the first direct threat of foreign military intervention in the election standoff, which has killed nearly 200 people since the November 28 vote.
swissinfo.ch and agencies