A Spanish journalist working in Colombia for almost two decades has disappeared while reporting a story on the illegal drugs industry and is feared kidnapped by Marxist rebels operating in the area, euronews quoted military sources as saying Monday.

Salud Hernandez, a journalist with Spain’s El Mundo and local newspapers, disappeared close to the town of El Tarra in the northern province of Norte de Santander on Saturday.

It is thought that Hernandez has been kidnapped by the National Liberation Army (ELN), the second biggest rebel group in Colombia, which has continued taking people hostage even while it seeks a peace accord with the government.

"I order priority and dedication from the armed forces in establishing where the journalist Salud Hernandez is," Colombian President Juan Manuel Santos said from his Twitter account.

The armed forces have activated a search operation for her in the area, according to a Tweet by the military.

Hernandez is known for her opinion columns that have been highly critical of Colombia’s insurgent groups.

Colombia has been in peace talks with the bigger rebel group, the Revolutionary Armed Forces of Colombia (FARC), since the end of 2012 and the ELN recently agreed to begin talks with the government.