Bogota - A group of Colombian soldiers saw three US citizens held hostage by leftist rebels since 2003, but did not attempt to free them and then lost track of the former contractors, Colombian Defence Minister Juan Manuel Santos said Monday.

Santos said the soldiers saw Thomas Howes, Keith Stansell and Marc Gonsalves as the three were taking a bath in the river Apaporis, in the southern Colombian province of Guaviare. The men were being watched by several members of the Revolutionary Armed Forces of Colombia (FARC).

The minister told Colombian radio station RCN that the soldiers were so close to the hostages that they heard them talking, although they could not understand what the three were saying because they spoke in English.

The soldiers told their superiors about the sighting. However, when a larger group returned to the place where the hostages had been bathing the rebels had left with the US citizens. The authorities then lost track of the group.

Santos did not say when the sighting happened, but stressed that the country's military forces continued to look for all hostages held by FARC, including former presidential candidate Ingrid Betancourt. The families of the kidnapped victims reject this strategy and claim that it is too risky for their loved ones.

Gonsalves, Stansell and Howes were kidnapped in February 2003, when the plane they were travelling in in southern Colombia crashed. They were under contract with the US Department of Defence and were active in anti-drug tasks in Colombia.

It remains unknown whether the plane crashed due to mechanical failure or was brought down by FARC. The three were travelling with fellow-US citizen Thomas Janis and with Colombian Army sergeant Luis Alcides Cruz, both of whom were reportedly killed by the rebels. (dpa)