The rebels demanded to see documents showing the men worked for private companies and letters from their relatives backing up their identities.
Uwe and Gunther Breuer, who are 69 and 72 years old, were seized in November. They had been touring South America in a jeep when they were taken in a remote area near the border with Venezuela.
In a statement published on their website, ELN (National Liberation Army) rebels asked the families of Gunther and Uwe Breuer to “send us truthful evidence that clarifies their ties with the captured men”.
They also demanded that “the German company, which these gentlemen said they work or worked for, show proof of their employment ties”.
The rebels also asked the German government to nominate an official to negotiate the release of the Breuer brothers.
The head of the anti-kidnapping unit of the Colombian police, Gen Humberto Guatibonza, said he had received information showing the two Germans were being held in a ELN rebel camp, but were healthy.
Map of Colombia
Colombian newsweekly Semana last week published a video showing the two brothers before they were seized.
The video shows them preparing their lunch on a camping stove by the side of a dirt road in central Colombia.
Gunther Breuer describes how he has been travelling the world for the past 18 months, including driving through Iran, Iraq, Australia and New Zealand.
He also talks about their plans to cross from Colombia into Venezuela.
He praises the Colombian people for their “friendliness” and says they have had no problems so far.
The fate of the Breuers became public last Monday when the ELN published a statement saying it had seized them in the Catatumbo region of Norte de Santander province.
The guerrillas said that “in the weeks they [Gunther and Uwe Breuer] have been held, they have not been able to justify their presence in the area, and we therefore consider them intelligence agents and will investigate them further”.
The rebels are also still holding a group of employees of an international mining firm they kidnapped in January, among them two Peruvians and a Canadian.
Colombian President Juan Manuel Santos has urged the ELN to free all its hostages immediately.
The ELN was formed in 1965, inspired by the Cuban revolution and Marxist ideology.
It has been seen as the more politically motivated of the two rebel groups in Colombia, but has over the past years increasingly resorted to drug trafficking, extortion and kidnapping for ransom to finance its insurgency.
The group says it is interested in engaging in peace talks with the government, but has refused to stop its attacks on civilian and military targets before any negotiations would start.
The government said it would not enter negotiations unless the ELN was willing to show “acts of peace” rather than just words.
Read more: http://www.foxbusiness.com/news/2013/02/11/colombia-stocks-drop-led-by-bancolombia-peso-gains/#ixzz2KdPg4yEX