The UN is moving non-essential staff out of Ivory Coast, following the state's disputed presidential election.
Some 460 staff would continue to carry out their duties from the Gambia, UN spokesman Martin Nesirky said.
Earlier, Botswana's President Khama Ian Khama urged African heads of state to strongly condemn what was happening.
He also told the BBC that President Laurent Gbagbo should step down, saying it was clear a majority of people had voted for his rival, Alassane Ouattara.
The World Bank and African Development Bank meanwhile said Ivory Coast had to resolve its political crisis or face having its aid frozen.
"We wish to continue working with the people of Ivory Coast in the fight against poverty but it is difficult to do so effectively in an environment of prolonged uncertainty and tension," said a joint statement.
"We will continue to closely monitor developments and reassess the usefulness and effectiveness of our programmes given the breakdown in governance."
The result of the 28 November presidential election run-off has left Ivory Coast with two presidents, who have each named separate cabinets.
The BBC's John James in Abidjan says there are even rumours that two sets of ambassadors will be appointed, creating even more confusion.
Western nations have thrown their support behind Mr Ouattara. Initial results issued by the electoral commission gave him a clear victory over Mr Gbagbo.
But the results were later overturned by the country's Constitutional Council, which awarded the victory to the incumbent.
Our correspondent says both sides are currently firming up their positions, leaving little room for compromise.
As the tension mounts, the UN announced on Monday that it would evacuate non-essential personnel - a decision that parallels similar moves by overseas companies like French Telecom and many of the cocoa exporters that work in the world's biggest producer, he adds.
The UN continues to have around 10,000 peacekeepers, some of whom are protecting Mr Ouattara and his self-declared government.
Several Western countries have also advised their citizens not to travel to the country, while Belgium has said it has deployed special forces personnel to protect its embassy.
On Monday night, the African Union's envoy, former South African President Thabo Mbeki, left Abidjan after two days of meetings with both sides.
He said he would submit a report to the African Union, and pleaded for both sides to help the regional grouping mediate.
"I'd like to say is that we indeed hope that the leadership of this country will do everything it can to make sure that peace is maintained, and indeed give space to the millions of other Africans represented by the African Union and other organisations to give them the space to come back to assist," he told reporters.
"Every effort should be made to ensure this transition to democracy succeeds."
Our correspondent says attention will now turn to the Economic Community Of West African States (Ecowas), which will hold an extraordinary meeting on Tuesday to consider the crisis.
Neither Mr Gbagbo nor Mr Ouattara have been invited.
On Monday, European Commission president Jose Manuel Barroso said the crisis risked stability and peace in the country and the region.
A spokeswoman for the EU's foreign policy chief, Catherine Ashton, said sanctions could be imposed if no solution was found.
International organisations and African leaders including Botswana's President Ian Khama have called on Mr Gbagbo to step down.
Mr Khama described the situation as a "real tragedy" and urged all African leaders to condemn what is happening.
"One would have hoped that by now, on the African continent, we would have gone past those days [of] coups and ridiculous situations like we have now in Ivory Coast," he told the BBC's Focus on Africa programme.
He also urged the international community not to broker a power-sharing agreement, as it did in Kenya and Zimbabwe.
"Elections there were hijacked by the ruling party and if that's going to happen every time someone wants to dispute an election result and then may stay in power by default through a mechanism of power sharing - it's wrong!" he explained.
Ivory Coast was split in two during a civil war in 2002.
This year's presidential election was the culmination of years of peace talks between the government and the rebel movement which largely controlled the north of the country.
It was hoped that the election would help to reunify the country, but analysts say the result and subsequent impasse threaten to set the peace process back years.
Mr Gbagbo is a southerner and is popular in Abidjan; Mr Ouattara draws most of his support from the north.