President Alvaro Uribe was booed and heckled in a most unusual public debate with a schoolteacher who walked halfway across Colombia to plead for a prisoner exchange with leftist rebels.

At one point during the extraordinary, impromptu appearance Thursday with his Cabinet members on the steps of Congress, Uribe denied being a front man for drug traffickers and far-right paramilitaries. Uribe even invited a young female heckler on stage and debated her, too, as about 3,000 people gathered around them in Bogota's central square.

The unprecedented political theater, broadcast live for more than two hours across the nation, was a reminder of how deeply divided Colombia remains over how to obtain freedom for the hostages held by leftist rebels.

It followed a 30-minute meeting Uribe held with schoolteacher Gustavo Moncayo, whose soldier son Pablo Emilio was captured a decade ago in a raid by the Revolutionary Armed Forces of Colombia, or FARC.

Moncayo and other captives' families want Uribe to exchange hundreds of imprisoned rebels for guerrilla-held captives. The rebels, however, are demanding that the military first temporarily quit a New York City-sized area of southwest Colombia, something Uribe once again rejected Thursday.

Uribe did say that if the FARC frees all its hostages, the government would demilitarize a zone for 90 days to begin peace talks. But that offer is almost certain to be rejected by the guerrillas.

Moncayo's 1,000-kilometer (600-mile) trek has received blanket media coverage in Colombia, inviting comparisons to India's independence leader Mohandas Gandhi. He vows to camp out on the square until the government and FARC agree on a prisoner swap.

Uribe met with Moncayo in his tent, then mounted the steps of Congress, where a microphone and podium had been set up, and immediately refuted the social studies teacher's criticisms.

"I am not front man for anyone, I don't have one dollar in a foreign bank," Uribe said, straining his voice to be heard against shouts of "Fascist," "Terrorist" and "Liar." Cabinet members and security officials flanked the president, nervously scanning the crowd.

Opponents say Uribe was an original promoter of the right-wing paramilitaries who killed more than 10,000 people in a terror campaign aimed at eradicating leftist rebels.

Uribe defended his hard line against the FARC, whose 45 prominent hostages include Moncayo's son, former presidential candidate Ingrid Betancourt and three U.S. defense contractors.

"The only reason for a demilitarized zone is for the criminals to hide from the security forces," shouted Uribe, jabbing his finger to make the point. "I won't hand over one millimeter to the criminals."

"We are trapped in the middle of the government and the FARC playing politics," said Moncayo, still wearing a metal chain around his neck, when Uribe invited him to speak. "Don't let our loved ones die in the jungles," he implored. "They deserve to live!"