A bomb attack blamed on Colombia’s leftist guerrillas has shut down the key Cano Limon-Covenas oil pipeline, a source at state-run oil company Ecopetrol which owns the pipeline, said on Thursday. Ecopetrol was not available for comment after normal business hours. It runs to the Covenas port on the Caribbean coast and also transports crude extracted by U.S. oil producer Occidental Petroleum Corp. It was restarted on May 25 after a two-month shutdown due to a series of bomb attacks in the same province. Colombia is Latin America’s fourth-biggest oil producer with daily output of around 1 million barrels.