UN chief Ban Ki-moon has warned supporters of Ivory Coast incumbent President Laurent Gbagbo not to attack his rival Alassane Ouattara's HQ.
An attack - threatened for Saturday - could spark civil war, he said.
Mr Ouattara, internationally recognised as winner of the presidential poll, is protected by UN soldiers in Abidjan.
Regional countries have threatened to oust Mr Gbagbo, but he says he will not leave voluntarily - and international pressure could trigger armed conflict.
"I do not believe at all in a civil war. But obviously, if the pressures continue as they have, they will push towards war, confrontation," he said in an interview for Euronews TV recorded on Tuesday and due to be broadcast on Friday.
He said his departure was not a guarantee for peace.
Mr Gbagbo says Mr Ouattara's victory is illegitimate. Both men have been sworn in as president.
On Wednesday Mr Gbagbo's Minister for Youth, Charles Ble Goude, urged followers to storm the Golf Hotel on Saturday "with our bare hands".
A statement from Mr Ban's office said he was "deeply alarmed" by Mr Ble Goude's call, adding that the UN mission would use all necessary means to protect Mr Ouattara.
"Any attack on the Golf Hotel could provoke widespread violence that could reignite civil war," the statement said.
"The secretary-general calls on all those who may be contemplating participation in the attack to refrain from such dangerous irresponsible action.
"He urges all the peace-loving citizens of [Ivory Coast] to contribute instead to the restoration of lasting stability and democracy in their country."
He said that an attack on peacekeepers constituted a crime under international law and its instigators would be held accountable.
Another UN official, Francis Deng, said allegations that homes of Gbagbo opponents had been marked to show their ethnicity were "extremely worrying".
On Wednesday Youssoufou Bamba, Ivory Coast's new ambassador to the UN appointed by Mr Ouattara, warned the country was "on the brink of genocide", and urged the UN to prevent the election being "stolen from the people".
West African regional bloc Ecowas is currently engaged with Mr Gbagbo in negotiations to resolve the crisis. The presidents of Benin, Sierra Leone and Cape Verde left without a deal on Wednesday but are expected to return on 3 January for more talks.
The Red Cross has said it is deeply concerned about the humanitarian situation in Ivory Coast.
The agency said that in the past month its workers had treated 590 wounded people, of whom about half had serious injuries.
It says thousands of people have been displaced within Ivory Coast and an even greater number have fled to neighbouring countries.
Ecowas has threatened in a statement to send in troops to force Mr Gbagbo to step down, but Mr Ble Goude warned against this.
"They should prepare themselves very well because we are thinking about totally liberating our country, and soon I will launch the final assault," he said.
Mr Ble Goude is renowned for his fiery rhetoric and has reportedly made such threats before without carrying them out.
But analysts have warned that inflammatory rhetoric could help push the nation back into civil war, seven years after a previous conflict resulted in it being divided between a rebel-run north and government-controlled south.
He is under UN sanctions for inciting violence in 2006.
The UN has some 9,500 peacekeepers in the country.
Mr Gbagbo has told them to leave, accusing them of interfering in Ivorian affairs. But the UN has refused to do so.
Mr Ouattara was initially declared the winner of the elections but his victory was overturned by the Constitutional Council.
The Council, led by an ally of Mr Gbagbo, ruled that votes in parts of the rebel New Forces-held north loyal to Mr Ouattara were invalid.