The Ivorian military has sealed the country's borders and blocked foreign media as tensions rise over the outcome of the presidential election run-off.
It comes after the Constitutional Council rejected a declaration by the electoral commission that opposition candidate Alassane Ouattara had won.
Supporters of President Laurent Gbagbo had tried to block the long-delayed result, alleging fraud in the north.
The UN Security Council asked both sides to show restraint.
"The air, land and sea border of the country are closed to all movement of people and goods," Ivorian military spokesman Babri Gohourou said.
The border would remain closed until further notice, Mr Gohourou added.
Shortly after, the military announced "the immediate suspension of all foreign news channels" in the country, including CNN, France24 and Radio France International FM.
The announcement of the result of Sunday's run-off had been much delayed, leading to heightened tension in the country.
Supporters of President Ggagbo had tried to block the result, saying there had been fraud in the north, the region where Mr Ouattara is most popular.
The north is also controlled by former rebels.
The head of the independent electoral commission (IEC) , Youssouf Bakayoko, said Mr Ouattara had won 54% of the vote, compared with 46% for Mr Gbagbo.
He was speaking under armed guard at a hotel, rather than from the commission's headquarters.
At about the same time, the head of the Constitutional Council, Paul Yao N'Dre, who is seen as being close to Mr Gbagbo, said it was taking over the declaration from the election commission.
"Because of disagreements on the results of some regions, the independent electoral commission wasn't able to give the provisional results," Mr N'Dre said.
"The Constitutional Council - responsible for sorting out disputes in presidential elections - finds itself in charge, to find a solution to the disagreements, and proclaim the definitive presidential election results."
The election was intended to reunify the world's largest cocoa producer which split in two after a civil war in 2002.
But the BBC's John James in Abidjan says there will now be a tug of war between the two bodies with the outcome unclear.
After a closed-door meeting, the members of the UN Security Council appealed to both sides to solve their difficulties peacefully.
The council members "reiterated their readiness to take the appropriate measures against those who obstruct the electoral process and, especially, the work of the IEC", the US ambassador to the UN, Susan Rice, said after the meeting.
French President Nicolas Sarkozy has urged the constitutional council to "respect the will clearly expressed by the Ivorian people", while the US White House said that "no party should be allowed to obstruct further the electoral process".
The International Criminal Court said it would be monitoring acts of violence.
Both the army and UN peacekeepers have been patrolling Abidjan's streets since Sunday to prevent an outbreak of violence.