It comes hours after the Constitutional Court 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," military spokesman Babri Gohourou said.
The border would remain closed until further notice, Mr Gohourou added.
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, which is controlled by former rebels and the region where Mr Ouattara is most popular.
Read the entire article at the BBC
we don't have a tag for the Ivory Coast, so I tried to tag this the best I could.