A bomb attack over the weekend by the Marxist ELN rebels has halted the flow of crude along Colombia’s second-largest oil pipeline, the Cano-Limon Covenas, sources from the military and state-run oil company Ecopetrol said on June 20.

The explosion took place on June 17 in a rural area of Saravena municipality, in the province of Arauca. Though the 485-mile (780-km) pipeline was stopped, operations at the Cano Limon Field, operated by U.S.-based Occidental Petroleum Corp. (NYSE: OXY), and exports were unaffected.

Attacks on oil infrastructure by the National Liberation Army, or ELN, have been frequent during the group’s five-decade war with the government. There have been 32 bombings so far this year, according to Ecopetrol, and frequently cause environmental damage.

The ELN has about 2,000 combatants and opposes the presence of multinational companies in the mining and oil sector, claiming that they seize natural resources without leaving benefits for the country’s population or economy.

President Juan Manuel Santos and the ELN in February launched formal peace negotiations in Ecuador, but the group has stepped up its attacks since.