(CNN) -- U.N. military helicopters Sunday pounded heavy weapons positions of fighters loyal to self-declared Ivory Coast President Laurent Gbagbo, United Nations officials said.
Choi Young-jin, head of the U.N. mission in the country, 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 U.N. forces are headquartered -- as well. "So we decided we cannot pass this moment without action," Choi said.
Together with the French military, U.N. forces targeted key positions. Choi said there were "several camps" belonging to the Gbagbo loyalists. "We are taking them out."
U.N. Secretary-General Ban Ki-moon said he ordered the military operation Sunday "to prevent the use of heavy weapons which threaten the civilian population of Abidjan and our peacekeepers."
The U.N. 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."
Gbagbo's forces had attacked the Golf Hotel Saturday as well. U.N. forces fired back at the time, said Hamadoun Toure, spokesman for the U.N. mission in Ivory Coast. "We stand ready to protect the Golf Hotel, as we have a mandate," he told CNN.
Toure added that Gbagbo loyalists continue to control three main areas -- the presidential palace, Gbagbo's residence and the state television station, RTI. He said the French military and U.N. forces are in charge of the Abidjan port.
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.
As Gbagbo has refused to cede power, the political stalemate has plunged the West African nation into crisis.
The U.N. human rights office said Friday that its investigators found more than 100 bodies over 24 hours in three Côte d'Ivoire towns.
Gbagbo's forces used a lull in fighting last week as a "trick" to reinforce their positions around the Abidjan, according to Alain Le Roy, the head of United Nations peacekeeping operations.
They said Tuesday they wanted a peaceful solution to the months-long fighting, but soon resumed shelling both the U.N. headquarters and the civilian population, Le Roy told reporters at the United Nations.
Since then, they have regained control of two central areas of Abidjan and fighting is continuing, Le Roy said Friday, after briefing the U.N. Security Council on developments in the cocoa-producing nation.
"They have clearly used the lull of Tuesday as a trick to reinforce their position," he said.
Mark Toner, acting deputy spokesman for the U.S. State Department, released a statement Saturday echoing that idea.
"It is clear that Gbagbo's attempts at negotiation this week were nothing more than a ruse to regroup and rearm. Gbagbo's continued attempt to force a result that he could not obtain at the ballot box reveals his callous disregard for the welfare of the Ivoirian people, who will again suffer amid renewed heavy fighting in Abidjan," he said.
Most areas of the capital, however, are now under U.N. or French military control, journalist Seyi Rhodes reported from the French military base in Port Bouet. The French military has been working to reconnect the disrupted water and electricity supply in what is the country's main city.
CNN's Aliza Kassim contributed to this report