Electricity and water have been cut to northern Ivory Coast - a region traditionally opposed to incumbent President Laurent Gbagbo, the UN says.
A UN official said the power company had said the supplies appears to have been cut for political reasons.
It comes after international radio stations including the BBC were taken off air without reason.
Meanwhile, the UN has apologised to Belarus for falsely alleging it broke an arms embargo against Ivory Coast.
Peacekeeping chief Alain Le Roy said the report which suggested Belarus had been supplying military equipment to disputed President Gbagbo "was a mistake".
Mr Gbagbo has refused to cede power to his rival, Alassane Ouattara, the internationally recognised winner of presidential elections last November.
Clashes between those supporting Mr Ouattara and those loyal to Mr Gbagbo have prompted the UN to warn the country is at risk of relapsing into civil war.
'No technical issues'
The national electric company said armed men had entered the building and ordered that the electricity for the entire northern half of the country be cut late on Monday, "even though no operational need existed and the network was healthy", according to a statement quoted by the Associated Press news agency.
Electricity is vital in rural Ivory Coast for powering wells to obtain water, correspondents say.
"The statement of the electricity company (says) this energy shortage is not due to technical issues," UN official Ndolamb Ngokwey told the BBC.
"This is what they said. They clearly said that it has to do with the political situation, so it was cut for political reasons."
Mr Ngokwey said the humanitarian crisis in Ivory Coast was worsening, and that 70,000 people had now fled the country - including 20,000 in the past two days.
Issia Doumbia, a spokesman for the New Forces rebels, which control the north and are loyal to Mr Ouattara, said millions of people are now without water or electricity.
"Things are turning bad - fast," he said.
In a separate development, a senior UN official said it should not have accused Belarus of sending three helicopters to Ivory Coast in breach of an international arms embargo, which has been in place since 2004.
Mr Le Roy said he had met with Belarussian officials and and "expressed our deep regret and our apologies for the damage caused to Belarus due to a wrong reporting from the mission".
He said Belarus, again and in writing, reaffirmed its "full compliance" with the arms embargo against Ivory Coast.
Also on Wednesday, international radio stations including the BBC and France's RFI were prevented from broadcasting on FM in the country.
The BBC said it did not know why the broadcasts had stopped and was investigating.
Supporters of Laurent Gbagbo have often accuse the Western media of bias.
The vote in November was supposed to reunify the country, which has been divided between north and south since a conflict in 2002.