Argentina is hosting a summit to try and defuse the latest in a series of rows between Venezuela and Colombia.Venezuela is ready to cut ties with its neighbour, after it agreed to allow the United States to use Colombian military bases. Argentine President Cristina Kirchner called for a new policy that will set out rules regarding foreign use of the South American Union’s bases. The summit is being broadcast live across the region at the request of Colombian president Alvaro Uribe. He says the US use of army bases is part of the fight against the illegal drug trade. His Venezuelan counterpart Hugo Chavez and his left-wing regional allies say US military involvement in the region is “imperialist aggression” and want the deal scrapped. Other countries, like Brazil, are demanding strict guarantees.