Bogota's mayor joined families of kidnap victims and about 300 school children Tuesday in a demonstration meant to increase pressure on the government to swap imprisoned rebels for guerrilla-held hostages.

The protest is "for the victims to pressure and hassle all they can and make those who have the power finally do something for this prisoner-swap," Mayor Luis Eduardo Garzon said.

The leftist Revolutionary Armed Forces of Colombia is holding around 60 prominent hostages, including former presidential candidate Ingrid Betancourt and three U.S. defense contractors. The rebels want all imprisoned rebels freed, including two held in the U.S., one of whom has already been convicted of drug-trafficking.

But with every new bomb, the prospects for a swap seem to fade away.

Authorities blamed rebels for a series of bombings that killed three and injured 30 over the weekend in the Pacific coast city of Buenaventura, calling it retaliation for the navy's recent killing of a rebel commander.

The rebels have yet to comment on the attacks, but President Alvaro Uribe on Monday ruled out a demilitarized zone in southwest Colombia, which has been a key rebel condition for any prisoner swap. "Terrorism will use the zone to mistreat the population and terrorists will use it as a refuge," said Uribe.

Meanwhile, the rebels have said there's no reason to stop fighting absent a government cease-fire. And in heavy combat in recent days, the army said late Monday that it killed 11 more rebels.