West African neighbours Ivory Coast and Liberia will launch a joint military operation by the end of the year along their volatile and porous border, the two nations’ presidents announced on Thursday.Western Ivory Coast has been the target of deadly raids blamed on supporters of former president Laurent Gbagbo, who was ousted in a civil war last year after he rejected the election victory of rival Alassane Ouattara.In a report published on Wednesday, U.N. investigators said pro-Gbagbo exiles were using Liberian territory as a "recruitment platform and rear base” for operations aiming to topple Ouattara, who is now president."I want to reassure you that we will continue our surveillance, our monitoring, our intelligence gathering and will take whatever action is necessary to ensure that peace and tranquillity prevails,” Liberian President Ellen Johnson Sirleaf said on Thursday following a meeting with Ouattara in Ivory Coast’s commercial capital Abidjan.Johnson Sirleaf and Ouattara said in a statement that their two governments had decided "to organise a joint military and security manoeuvre before the end of 2012”.Interior, defence and foreign affairs ministers from the two countries have met three times in recent months to calm tensions over the border violence.While Gbagbo is currently in The Hague charged with crimes against humanity by the International Criminal Court, many of his top political and military allies are living in exile in neighbouring West African nations.