Colombian officials released newly seized videos of rebel-held hostages Friday — among them three U.S. defense contractors and a former presidential candidate — the first images in years providing evidence the captives may be alive.

The tapes were seized during the arrest Thursday evening in Bogota of three suspected urban members of the Revolutionary Armed Forces of Colombia, known as the FARC, said Luis Carlos Restrepo, the government's peace commissioner.

Also recovered were a series of letters apparently written by the hostages, including what appeared to be the will of U.S. contractor Thomas Howes.

The videos were apparently recorded as recently as late October, Restrepo said.

The hostages' families welcomed the proof that their loved ones were still alive after years of uncertainty but expressed frustration at the lack of progress toward their release.

"I knew my son was alive, knew they were all alive, but I needed to see him," said Jo Rosano, the mother of the U.S. contractor Marc Gonsalves, who has been kidnapped since 2003. "He's lost some hair, lost some weight, but he looks good."

She added, "It angers me he is being held for no good reason against his will."

The U.S., French and Colombian governments had demanded evidence the captives were alive during Venezuelan President Hugo Chavez's ill-fated mediation effort to win the release of 45 high-profile hostages held by the FARC.

The FARC never delivered the material, and Colombian President Alvaro Uribe abruptly ended the Venezuelan leader's mediation role last week, saying Chavez had overstepped his bounds by directly contacting the head of Colombia's army.

Some of the families of the kidnapped videos pleaded with Uribe to reconcile with Chavez and restart the talks.

"Please start the dialogue ... I'm begging you," said Yolanda Pulecio, mother of former presidential candidate Ingrid Betancourt. "I had the feeling that Ingrid was alive, but I also knew the conditions" of her captivity.

The videotapes, which were played at a news conference without sound, showed an extremely gaunt Betancourt, a dual French national seized while campaigning in 2002, apparently chained and in front of a jungle backdrop.

Betancourt has long hair and stares blankly at the ground. No images of her had been seen since 2003.

Betancourt has become a cause celebre in France and that that country's president called the video "undeniable" evidence that Betancourt "is alive."

"This encourages us to boost our efforts to win her release," President Nicolas Sarkozy said.

The Americans — Howes, Keith Stansell and Gonsalves — were abducted by the FARC after their surveillance plane went down in a southern Colombia jungle in 2003.

In the images, each American briefly stands alone on the screen, all dressed in T-shirts and rubber boots typical of the rebels, also against a jungle backdrop, looking haggard. In one shot, a rebel stands guard in the background, his hand clasping his rifle.

The rebels had not released any images of them since 2003. The U.S. Embassy in Bogota has called the three Americans the longest-held U.S. hostages currently in captivity.

The FARC, which uses kidnapping as a tool to raise money and pressure the government, are offering to release these and dozens of other high-profile hostages in exchange for the freeing of hundreds of rebels from Colombian and U.S. prisons. Some hostages have endured a decade in FARC captivity.

The Colombian government said the tapes of Betancourt carried the time stamp of Oct. 24, 2007. The tape of the Americans carried the date of the Jan. 1, 2007. But a kidnapped Colombia soldier who appeared on the same tape said the recording was being made on Oct. 23.

Betancourt's sister, Astrid, said the October dates indicate the rebels had intended to give the footage to Chavez.

In justifying its decision to end Chavez's role as mediator, the Colombian government said the FARC had failed to respond to the Venezuelan president's entreaties for proof of life.

"I think the FARC was getting this evidence together for Chavez," Rosano said. "Why else would they be recording these videos now after so many years?"

Restrepo said the five tapes also showed images of 12 Colombians, mainly police and soldiers, and that other seized documents included a series of letters apparently written by hostages.

One undated letter was from Howes to his wife, and another, dated Nov. 26, 2006, was his will, the government said. Betancourt wrote a letter to her mother, dated Oct. 24, 2007. Another note was from Gonsalves to the military commander of the FARC, known as "Mono Jojoy," dated Oct. 23, 2007. The government did not reveal the letters' contents.

Chavez's dismissal from the process has raised tensions between the two countries, with the Venezuelan leader vowing he would have "no type of relationship" with the Colombian government as long as Uribe was president.

Uribe, whose father was killed by the FARC, has advocated military rescues of the hostages, but families fear their loved ones would be killed in crossfire. Since he took office in 2002, Uribe's administration has had no face-to-face meetings with the rebels.