UN Special Representative Young-Jin Choi said pro-Gbagbo forces were shelling the Golf Hotel in Abidjan, where the country's internationally recognized president Alassane Ouattara is staying, and "today they began to shell our quarters", the section of the hotel in which the UN forces are headquartered, as well. "So we decided we cannot pass this moment without action," Choi said.

UN Secretary-General Ban Ki-moon said he ordered the military operation "to prevent the use of heavy weapons which threaten the civilian population of Abidjan and our peacekeepers."

The UN mission does not extend to extracting Gbagbo from his residence, Choi said. It would be up to pro-Ouattara forces to oust Gbagbo, he said.

Ban renewed his call for Gbagbo "to step aside immediately."

"Civilians are bearing the brunt of the violence," the secretary-general said. "The fighting must stop. Mr. Gbagbo needs to step aside immediately."

Violence erupted after Ivory Coast's disputed presidential election in November and escalated into all-out war when Ouattara's forces launched an offensive that brought them into Abidjan.