A senior Colombian official says two Germans detained by the country's No. 2 leftist rebel group are brothers aged 72 and 69 who were touring South America.

The official said Guenther Otto Breuer and his younger brother Uwe were engaged in "ecotourism" when seized several weeks ago in the northeastern municipality of Convencion.

The rebel National Liberation Army, or ELN, announced Monday on its website that it would consider both men spies unless the contrary is proven.

The Colombian official spoke on condition of anonymity due to the subject's sensitivity. A German Embassy spokesman declined comment.

The ELN kidnapped six gold prospectors, including a Canadian and two Peruvians, on Jan. 18.

It has been seeking to join a peace process involving the government and Colombia's top rebel band.