Heavy fighting broke out on 31 March 2011 as forces of Alassane Ouattara advanced on Abidjan from several directions. The United Nations peacekeepers took control of Abidjan's airport when Gbagbo's forces abandoned it and United Nations forces were also reported to be carrying out protective security operations in the city. The UN peacekeeping mission said its headquarters were fired on by Gbabgo's special forces on 31 March, and returned fire in an exchange lasting about three hours. UN convoys have also come under attack by Gbagbo loyalists four times since 31 March, with three peacekeepers injured in one of the attacks. The peacekeepers had exchanged fire with Gbagbo loyalists in several parts of the city.