Colombia's ELN rebels have begun the process of releasing a hostage at the center of a dispute that is threatening planned peace talks with the government, a top official said Thursday.

"We have been informed by the Red Cross that the operation to free (hostage ex-lawmaker Odin Sanchez) has begun," said Juan Camilo Restrepo, the government's chief negotiator for the talks, which President Juan Manuel Santos called off hours before they were due to open.