The smaller of Colombia's two main guerrilla groups acknowledged on Monday that it was behind last week's kidnapping of two pipeline company employees in the oil-rich northeastern province of Arauca.

The claim of responsibility came in the form of a message sent to the families of journalist Elida Parra Alfonso and environmental engineer Gina Paola Uribe by the Eastern War Front of the National Liberation Army, or ELN.

The women were abducted separately last Tuesday from their homes in the city of Saravena.

Parra and Uribe do community outreach work for contractors on the Bicentennial Pipeline, or OBC, which - once completed - will transport crude from oil fields in Arauca to the Caribbean port of Coveñas.

In the statement sent to the captives' families, the ELN also took responsibility for the recent killing of Ricardo Mora, a manager of OBC contractor Sicim, and for a bombing at a oil pumping station.

The OBC is being built by a consortium made up of Colombia's state-owned Ecopetrol and seven multinationals, including Canadian firms Pacific Rubiales Energy and Petrominerales.

The ELN vowed to continue its "political-military" action against the oil sector.

"Every megaproject of imperialism, multinationals and the oligarchy are and will be a military objective of the ELN, because they only benefit the capitalist system," the rebel group said.

The ELN statement did not set forth any demands for the release of Uribe and Parra.

Colombia's second-largest insurgency kidnapped 11 employees of Consorcio Casanare Avanzada, one of the contracting firms on the OBC, for a week earlier this year.

The rebels said in March that they are willing to end their offensive against the oil industry if the government agrees to make some areas off-limits and to levy a $10 per barrel "social tax" on crude production. EFE