The African Union has suspended Ivory Coast, following a disputed presidential election in the West African nation.
AU official Ramtane Lamamra said Ivory Coast would remain suspended until opposition candidate Alassane Ouattara "takes over" from Laurent Gbagbo.
The UN Security Council earlier said Mr Ouattara had won last month's poll.
However, Mr Gbagbo - backed by the army - is defying international pressure and continuing to cling to power.
In a separate development, the US warned that it would consider sanctions against Mr Gbagbo if he refused to step down.
Mr Lamamra made the announcement on Thursday, after an AU meeting at its headquarters in Addis Ababa, Ethiopia.
Mr Lamamra said the decision had been taken by the council of the 53-nation bloc, describing Mr Ouattara as "a democratically elected president".
Earlier, West African regional bloc Ecowas also suspended Ivory Coast.
The move is largely about prestige, but if these measures are backed by the West African Central Bank - which is yet to respond to a request from Mr Ouattara to gain control of the Ivorian government accounts held there - it would make it very difficult for Mr Gbagbo to keep control of the state, the BBC's John James in Abidjan reports.
Last Thursday, Ivory Coast's Independent Electoral Commission (IEC) declared that Mr Ouattara had won the 28 November run-off by 54.1% to 45.9%.
But Mr Gbagbo and his supporters alleged the ballot had been fraudulent in some northern regions, which are under the control of the New Forces rebels who support Mr Ouattara.
The Constitutional Council - run by Mr Gbagbo's ally - annulled votes in these areas and declared Mr Gbagbo the winner, with 51% of the votes.
Both Mr Gbagbo and Mr Ouattara have since sworn themselves in and named their rival Cabinets, heightening tension in the country.
Mr Ouattara - who has the backing of the US and France among other nations - is operating from a luxury hotel in Abidjan, guarded by UN peacekeepers. His power does not extend much further than the perimeter walls of the hotel.
However, Mr Gbagbo - who seems determined to hold on to power in the face of all opposition - must at least recognise that almost every international organisation, government and financial institution recognises his rival as the winner of the elections, our correspondent says.
He adds that there remains a real potential for violence, with thousands of unarmed militia and rebel soldiers allied to each side.
The election was intended to reunify the world's largest cocoa producer after a civil war in 2002.