A presidential candidate who is a severe critic of Colombia's leftist guerrillas was abducted by the rebels as she headed into a zone they once controlled, her campaign spokeswoman said Sunday.

Ingrid Betancourt disappeared after setting out for San Vicente del Caguan, a former rebel stronghold that was seized by government troops Saturday in an offensive to retake a large swathe of rebel-controlled territory.

Betancourt and her campaign manager Clara Rojas were kidnapped Saturday by rebels with the Revolutionary Armed Forces of Colombia, or FARC, spokeswoman Diana Rodriguez told The Associated Press.

Rodriguez said the rebels released two journalists -- one French, the other Colombian -- and a campaign coordinator who had been accompanying Betancourt and Rojas. The three returned safely to an army base in the city of Florencia, where Betancourt began her trip, Rodriguez said.

Colombia's government said it had warned Betancourt, a former Senator, not to make the trip to San Vicente because it was too dangerous.

Interior Minister Armando Estrada called on the rebels to release Betancourt. "We ask those who are holding her to respect her life and release her quickly so she can resume her advocacy work," he said.

Estrada said the government was searching for her and was doing what it could to establish security in the war zone.

Betancourt was one of a number of candidates in the elections set for next month who had planned to enter the former rebel-run territory to show their support as the government moves to retake the area.

President Andres Pastrana had ceded the zone, an area twice the size of New Jersey in southern Colombia, to the FARC three years ago in hopes of brokering an end to the country's 38-year war. But last week he declared the peace process collapsed, citing repeated FARC attacks on military and civilian targets, and on Friday thousands of troops began moving into the area.

The troops moved into San Vicente, the main town in the region of 100,000 people, before dawn on Saturday.

Estrada urged other candidates not to visit the area for the moment, and two candidates postponed planned trips.

"It is good that politicians are doing what they can to draw support for their campaigns and their causes ... but it was not necessary to make that trip in those conditions," Estrada said.

Betancourt and her group were snatched in a volatile area just outside the zone, on a highway that goes through a string of hamlets, some dominated by rebels, others by right-wing paramilitaries.

Adair Lamprea, the campaign coordinator later freed, told The Associated Press that the candidate and her group ran into a rebel roadblock constructed of two buses packed with explosives. Other guerrillas soon arrived in several trucks.

"They were waiting for orders about what to do with Ingrid," Lamprea, 31, said. "There was a Red Cross truck (at the roadblock) when we arrived, but they told them to go back."

Eventually, the rebels ordered Betancourt into one truck and Rojas into another, Lamprea said. "When (Betancourt) got into that truck, she appeared strong, just like she always is, but nervous," he said.

"They freed the rest of us at night and told us that they had the person they wanted and that we weren't part of the problem," Lamprea continued. "They dropped us off somewhere and we walked and walked until a truck came by and picked us up. All night there was bombing, and we could feel it strongly. It was horrible."

Betancourt had planned to meet with San Vicente Mayor Nestor Leon Ramirez, a member of her political party. She had told reporters she was determined to stage a rally in San Vicente for "respect for human rights."

Betancourt's husband, Juan Carlos Lecompte, said Betancourt felt she needed to be with the people of San Vicente "during the good and the bad."

Betancourt is well known but was trailing in the field of more than 10 candidates trying to replace Pastrana, who cannot run for re-election under Colombian law.

She was one of four presidential candidates who traveled into guerrilla territory in February to cajole rebel and government peace negotiators to make progress.

"What were you thinking when you decided to join the guerrillas?" she asked rebel leaders during a nationally televised forum in the zone in February. "Did you think the guerrillas would be involved in cocaine?"

The FARC taxes cocaine profits to finance its war. One of its key demands is the withdrawal of U.S. military personnel who are training Colombian anti-narcotics troops.