Colombia's largest rebel group killed three soldiers and responded to a government offensive by sabotaging utility lines, roads and bridges in their former safe haven.

One army soldier was killed Monday when troops fired on Revolutionary Armed Forces of Colombia, or FARC, rebels tampering with power lines. Two other soldiers died trying to defuse a bomb on a bus blocking a key highway.

In Bogota, 190 miles north of the war zone, guerrillas detonated a bomb at a reservoir serving the capital city. The attack didn't affect water supplies, Mayor Antanas Mockus said.
``This is the kind of thing that even countries fighting other countries don't do,'' the disgusted mayor said.

In 1998, the government gave the FARC a Switzerland-sized parcel of land to lure the group to peace talks. But when the FARC hijacked a civilian airliner Wednesday and kidnapped a senator, President Andres Pastrana canceled talks, ordered the rebels out of the zone and sent his troops in.

Since then, rebels have toppled utility pylons both inside and outside the zone in southern Colombia, blacking out or forcing electricity rationing in at least 56 towns, the energy ministry said.

San Vicente del Caguan — the former rebel capital that was the first town occupied by army troops on Saturday — has been among those hit the hardest. A downed bridge and rebel roadblocks virtually have isolated the sweltering town from the rest of the country. Food stocks are dwindling and drinking water is scarce.

Mayor Nestor Ramirez declared a local state of emergency and asked troops to supply his town of 22,000 by using military helicopters.

Fearing rebel attacks, the government temporarily suspended flights by an Air Force-owned airline to the nearest city, Florencia. Rebel roadblocks also make the road to Florencia dangerous.

``The situation generated by the violence of the past few days took us by surprise,'' said Ramirez, a colleague of presidential candidate Ingrid Betancourt, who was kidnapped by rebels Saturday while driving to San Vicente from Florencia.

Troops occupied the former rebel town of Vista Hermosa on Sunday, only to find that guerrillas downed a nearby utility tower and blacked out the town. Parts of eastern Ecuador also experienced blackouts.

Rebels planted land mines around the wreckage, hampering repairs.

``It scares us a lot to be here,'' said Hector Correa, chief of a repair crew. ``They used to explode them on top and we could rebuild them. But now they hit them at the bottom, and we have to start over completely.''

The FARC has blown up 11 bridges since Thursday, disrupting transportation throughout the region.

``The guerrillas have created a grave situation'' for many in southern Colombia, Transport Minister Gustavo Canal said.

Colombian news media reported Monday that the FARC executed five people in La Macarena, which the army had yet to reach. The reasons for the killings were not known.

Pastrana was reviewing the volatile situation with his Cabinet and ``looking for other ways to stop the terrorism and abductions,'' Justice Minister Romulo Gonzalez said.

In Washington, President Bush's national security aides planned to meet this week to discuss helping Colombia's military.

U.S. intelligence sharing is being increased and deliveries of spare parts for U.S. helicopters are being accelerated. Officials also were addressing an existing ban on U.S. military assistance for anything other than counter-narcotics activities.

The FARC, a smaller rebel group called the ELN and right-wing paramilitary forces known as the AUC are on the State Department's list of Foreign Terrorist Organizations.

Interior Minister Armando Estrada said the government received a communique saying Betancourt would be held until the government freed detained guerrillas. He said officials were trying to authenticate the statement signed by a senior rebel commander.

Betancourt's kidnapping aroused international concern for the security of candidates in the March legislative elections and May 26 presidential vote.

U.N. Secretary-General Kofi Annan condemned Betancourt's kidnapping, saying it undermines upcoming elections and intimidates civilians.

Cesar Gaviria, secretary general of the Organization of American States, said Monday ``the Colombian electoral process will prevail and will remain unshakable.''