The alleged assassination plot by Colombia's FARC rebels against ex-president Alvaro Uribe is "unacceptable" and will "destroy" efforts towards negotiating peace, the chief government negotiator said Wednesday. This scenario will completely destroy the viability of the process," said Humberto de la Calle, a former vice-president, in a Bogota forum. The remarks come one day after Colombia said it was tightening security following the discovery of a FARC rebel plot to murder Uribe, who has been a vehement critic of the peace talks. "If in Havana, we talked about tolerance, about pluralism, the FARC should have brought guarantees of non-aggression," de la Calle said.