The government of disputed President Laurent Gbagbo has banned UN and French peacekeeping aircraft from flying over, or landing in Ivory Coast.
The announcement came as Alassane Ouattara, recognised by the UN as the winner of November's poll, went to Ethiopia for a meeting on the crisis.
The African Union is set to call for Mr Ouattara to lead a unity government, the BBC understands.
Mr Gbagbo has refused to attend the African Union gathering.
The BBC's Uduak Amimo at the AU summit in the Ethiopian capital, Addis Ababa, says it is not clear if the proposed plan for a government of national unity would retain a role for Mr Gbagbo but it would certainly include some of his loyalists.
A team of five African heads of state has been considering how to resolve the political impasse amid warnings the country is sliding back into civil war.
Last year's long-delayed elections had been supposed to reunify the country - once the richest in West Africa - which has been divided since a 2002 civil war.
The UN-backed electoral commission says Mr Ouattara won presidential elections in November, but the Constitutional Council overruled it, citing rigging in the north.
The BBC's John James in the main city of Abidjan says the flight ban may be an attempt to stop Mr Ouattara from returning to Ivory Coast.
The no-fly zone will not stop him but it will make it more difficult for him to get to Abidjan and the Golf Hotel, where he has been under the protection of UN peacekeepers, he says.
It is the first time Mr Ouattara has left the hotel since the results were declared in December.
The statement read out on state television said "exceptional overflights or landings must be previously authorised by the transport ministry".
Our reporter says the UN has yet to give a formal response, but on Thursday morning a UN helicopter was flying over Abidjan in clear breach of the order.
Mr Ouattara's allies say the ban carries no legal value because Mr Gbagbo is no longer in power.
Mr Gbagbo has sent two envoys to the AU meeting, but since December he has rejected offers of exile and other mediation attempts.
His security forces have crushed opposition rallies, using live ammunition on unarmed protesters.
The opposition has reacted by re-arming.
The UN says fighting in Abidjan has forced 300,000 people to flee from northern suburbs of the city in recent weeks.
Our correspondent says Ivorians are not hopeful that the AU can achieve a breakthrough.
There are growing signs that the pro-Ouattara forces that control the northern half of the country will start moving south in the coming days, he says.