Colombian rebels have released videos indicating that four policemen and a soldier they have been holding since the late 1990s are still alive.
In the videos, the men urge officials to hold talks with the rebels.
It was not clear when the recordings were made but they have emerged just two weeks before the second round of Colombia's presidential election.
Candidates Juan Manuel Santos and Antanas Mockus both say a condition for talks is an end to hostage-taking.
The videos came to light via Senator Piedad Cordoba, who has previously played a key role in bringing about the release of hostages held by the Revolutionary Armed Forces of Colombia (Farc).
One of the hostages shown in the videos is Cpl Jose Libio Martinez. He was seized in 1997 together with Sgt Pablo Emilio Moncayo, who was freed earlier this year.
"I don't want to be the last man freed, but rather the last man taken hostage," he said.
"I wish to tell President Alvaro Uribe and the presidential candidates, Juan Manual Santos and Antanas Mockus, that talks with insurgent groups should lead to an end to kidnapping."
In the video, he also sent a message to his son, Johan Steven, 12, who was born after his father was kidnapped by the Farc.
The other hostages, police officers Edgar Yesid Duarte, Elkin Hernandez Rivas, Alvaro Jose Moreno and Luis Alberto Erazo, have also been in captivity for more than 10 years.
Police Major Hernandez Rivas called on the government and the Farc to negotiate to ensure their release and that of 18 other members of the security forces.
The guerrillas want to swap the hostages for jailed rebels.
Meanwhile, Farc guerrillas said they were holding a marine who disappeared a week ago during an ambush in the southern province of Caqueta that left nine marines dead.
In another development, five people taken hostage last week have been found alive in the jungle in Narino province.
Their kidnapping was blamed on Colombia's smaller rebel group, the National Liberation Army (ELN).
Both Mr Santos and Mr Mockus have said that they will continue President Uribe's security policies.
But the rebel activity is likely to boost Mr Santos's vote, says the BBC's Jeremy McDermott in Colombia.
The former defence minister was far ahead of Mr Mockus, the Green party candidate, in the first round at the end of May.