Colombia 's largest rebel group has freed some of the world's longest-held hostages, ending more than a decade of jungle captivity for 10 police officers and soldiers.

The captives were released by the Revolutionary Armed Forces of Colombia, or Farc, in a long-planned operation overseen by the Red Cross, the Brazilian government and a former Colombian senator, Piedad Cordoba.

President Juan Manuel Santos called the release "a step in the right direction, a very important step" but cautioned against "pure speculation" that it presaged formal peace talks.

The six police officers and four soldiers were picked up from the jungles of southern Colombia by a helicopter provided and manned by the Brazilian air force.

The freed men - seeming well fed and relatively healthy - were greeted by dozens of family members in the airport, in some cases meeting teenage children they had not seen since they were babies.

Some saluted as they crossed the runway, carrying pets they had brought from the jungle: a peccary, a monkey and two small birds. One wrapped himself in a Colombian flag.

Originally the plan had been to free the hostages in two groups over two days. It was only after the helicopter took off to pick up the first group, that it was revealed that all 10 would be freed.

"I shouted! I jumped up and down!" said Olivia Solarte when she first heard her 41-year-old police officer son, Trujillo, had been freed after nearly 13 years.

One of the freed men, army sergeant Robinson Salcedo Guarín, said that he and his fellow captives only learned they were to be released via a news bulletin that interrupted a football match they were listening to on the radio.

The 10 were a reminder of a different time in Colombia's conflict, an era when the Farc mounted huge operations overrunning police and military bases. The longest-held hostage, police sergeant Luis Alfonso Beltran, was captured in the battle of El Billar in 1998 in which 64 police officers were killed and 43 taken prisoner.

Doris Moreno said her brother, army sergeant Luis Alfredo Moreno, who was kidnapped in 1998, did not recognise a mobile phone. "He saw my mobile and asked me what it was," she said. "He didn't know that mobiles existed, didn't know how to pick it up and speak with it."

The release followed a series of messages from Farc leaders - including a promise to stop kidnapping for ransom - signalling a willingness to launch talks to end the country's five-decade civil war. Cordoba said that rebels at the release had told her: "The next time we meet, it must be to talk peace."

Former president Ernesto Samper said that he hoped the rebels' move would be recognised as an act of peace and called on the government to start a process of national reconciliation.

"This is a gesture that shouldn't be underestimated," conflict analyst Juan Carlos Palou told Associated Press. "The promise that they will no longer kidnap for ransom implies to me that the government really should take it as a sign that Farc really is interested in talks and moving ahead with a process to end the conflict," he said.

But Santos, who has faced sustained criticism from former president Álvaro Uribe Vélez over the country's security situation, rejected international mediation for peace talks and called on Farc to release or provide information on "hundreds" of civilian hostages.

"When the government considers that the conditions are right and there are guarantees to start a process that will end the conflict, the country will know," he said.

While there are no reliable figures on how many hostages Farc is currently holding, dozens of civilians are thought to have died in captivity.