Forces loyal to besieged Ivory Coast leader Laurent Gbagbo have regained ground in Abidjan and now fully control the Plateau and Cocody areas of the city.
That is according to UN peacekeeping chief Alain Le Roy, who said the fighting had reached a "stalemate".
Mr Gbagbo remains holed up in his bunker in Abidjan, refusing to hand power to the democratically elected leader Alassane Ouattara.
Military forces loyal to Mr Ouattara have surrounded the compound, but he has said they will not attack his opponent.
Instead, he said they would focus on getting life back to normal on the streets of the country's commercial capital, where many have been forced to hide indoors from heavy arms fire.
In a televised address on Thursday, Mr Ouattara said he had asked for EU sanctions on the main ports and other businesses to be lifted to help the country recover.
Mr Le Roy said Mr Gbagbo's forces took advantage of a break in fighting on Tuesday for peace talks to reinforce their positions.
The talks have so far led nowhere.
"We understand that since that time the forces of Mr Gbagbo have regained terrain and they have full control of the Plateau and Cocody areas," he said.
He added: "We have seen heavy weapons to be transferred to the Cocody area, including this morning."
Mr Le Roy said Mr Gbagbo's forces were edging closer to the Golf Hotel, where Mr Ouattara has been based since winning the presidential election on November 28 last year.
Earlier the UN said more than 100 bodies had been found in three different towns in the west of the country, where tensions have risen as the fight for the presidency continues.
Some of the victims had been burned alive and others had been thrown down a well.
The UN said the dead were all believed to be Guerres, who have been traditional supporters of the incumbent president.
The discovery of the bodies came after the International Rescue Committee (IRC) warned chaos was escalating.
More than 1,500 people have died since the violence began.