Y.J. Choi, the U.N. special envoy to Ivory Coast, said snipers loyal to incumbent President Laurent Gbagbo were firing directly at peacekeepers in the country.
"We are planning action, we can no longer condone (Gbagbo's forces) reckless and mindless attack on civilians and the United Nations blue helmets with heavy weapons," he told the BBC.
He added that the 9,000 peacekeepers stationed in Ivory Coast don't have a mandate to remove Gbagbo from power but they are permitted to respond to military aggression with force.
Gbagbo refuses to step down despite international recognition that his rival Alassane Ouattara won a November election meant to unite a country divided by civil war.
Forces loyal to Ouattara are said to be on the verge of launching a major assault on Gbagbo forces in Abidjan, the commercial capital of Ivory Coast. French military forces took control of the main airport after Paris said it was considering evacuating its citizens from the country.
The International Committee for the Red Cross announced Monday that at least 800 people were killed in the Ivorian town of Duekoue last week.
Duekoue is a strategic area because of its proximity to the cocoa-producing areas of the country. Ivory Coast is the world's largest cocoa producer.
The International Crisis Group said recently the conflict in Ivory Coast bore the hallmarks of civil war.