Colombia's second-largest guerrilla group has asked for proof that two German men it holds hostage are tourists and not intelligence agents, the rebels said on Monday.
The National Liberation Army, known as the ELN, captured the two men in November 2012, the government says, in a sparsely populated area near the Venezuelan border but only made the kidnapping public earlier this month.
Germany said that the two were retirees and had been traveling as tourists.
"We ask their families to send us truthful evidence that clarifies their ties with the captured men. Also we ask the German company which, is said, these gentlemen work or worked for, to show proof of their employment ties," the group said in a statement published on Monday on its website.
The ELN, considered a terrorist group by the United States and European Union, asked the German government to name one of their officials in Colombia to facilitate the men's liberation.
The rebel group is not included in peace talks in Cuba between the Colombian government and the nation's biggest insurgent group the FARC, or the Revolutionary Armed Forces of Colombia, to end to five decades of war.
The ELN, which security sources say may be stepping up pressure on the government so it can be included in the peace talks, also seized a Canadian and two Peruvian gold-mine workers in north Colombia last month.
(Reporting by Luis Jaime Acosta; Editing by Philip Barbara)