Hours from a government deadline, a United Nations envoy met with commanders of Colombia's largest leftist rebel army Saturday to try to revive peace negotiations.

Envoy James LeMoyne held a second day of talks in a rebel safe haven amid cautious hopes that he could patch up the 3-year-old peace process between the Revolutionary Armed Forces of Colombia and the government.

"We think that we're advancing, but we're still working," said LeMoyne, who warned earlier that the South American country hung between peace and all-out war.

A rebel commander involved in the talks was seen burning a document, something the rebels have traditionally done with working papers during the negotiations.

A few hours earlier, a car bomb exploded near the wall of a military base a few miles north of the rebel haven, injuring 15 civilians, the army news agency said. Troops had been arriving at the base in the town of Granada ahead of the deadline. No one immediately claimed responsibility for the blast.

President Andres Pastrana declared peace efforts over Wednesday and threatened to send troops back into the rebel haven. But the next day he gave LeMoyne until Saturday night to restart peace talks, which the rebels suspended in October after the army instituted security controls outside the zone.

If LeMoyne failed to achieve a "positive result," Pastrana said he would give the rebels 48 hours to abandon the five main towns in the Switzerland-sized safe haven in southern Colombia. Army troops were ready to move into the zone, which many feared would greatly escalate the 38-year-old civil war.

Prayers for peace were held in the Roman Catholic church in the zone's main town, San Vicente del Caguan. The church was packed with local politicians, firefighters, businessmen, ranchers, housewives and children carrying small white paper signs saying "Peace."

"In this crucial moment of the history of our country, we need tolerance," said the Rev. Miguel Angel Serna, who called for dialogue rather than fighting.

He lashed out at military leaders of both sides for waging a war that kills some 3,500 people every year.

"Good people — humble campesinos, humble rebel fighters and humble soldiers — have died in combat, but not the big leaders," Serna said. "It is the good who fall."

At the closest military base to the zone, an army commander said reinforcements had poured in over the past few days.

Army Maj. Geraldo Cano, chief of operations for the Hunter Battalion based in the town of Florencia, said the soldiers were ready to move into the zone at a moment's notice.

A veteran rebel, interviewed in San Vicente, echoed pledges that the insurgents would pull back from the five towns if Pastrana ended the safe haven, which he agreed to three years ago as a condition for starting peace talks. But the rebel said the countryside of pastureland and thick jungle was another matter.

"If the government wants the rural areas — even a place five minutes from here — they'll have to fight for it," said Mauricio, who wouldn't give his last name.

Meanwhile, government negotiator Camilo Gomez began a second day of talks in Cuba with Colombia's smaller rebel movement, the National Liberation Army. The discussions are aimed at creating a framework for formal negotiations.