BOGOTA -- President Alvaro Uribe has urged members of the Colombian military not to spare any efforts in bringing freedom to 26 civilians taken hostage by leftist rebels in the northwest of the war-ravaged country.

"It is necessary that these operations produce quick results," Uribe told soldiers participating in a rescue operation launched in the wake of the abduction of the hostages by suspected rebels of the National Liberation Army (ELN), the second-largest guerrilla force.

Uribe, who made a surprise visit to Choco Province Friday, said hostage taking was not only causing immense suffering to the local population but was also undermining the tourism industry.

The hostages -- presumably all Colombian nationals -- include local government workers, several businessmen and at least one labor union leader, according to police officials.

The army rescue operation is currently focusing on Utria National Park, where the captives, taken hostage Tuesday, are believed to be held.

Uribe told local residents to cooperate with the military in finding the hostages and pushing the rebels away from the country's Pacific coast.

"I invite all compatriots who live along the Pacific coast, from the border with Panama to the border with Ecuador, to back our defense force in clearing the area from the rebels," the president said.

On Thursday, the government warned that Colombia's largest rebel group is gearing up for a major offensive with advanced weapons, AFP reported.

In a letter sent to the constitutional court hours after the guerrillas rejected his offer of UN-led mediation to end the country's civil war Uribe's administration said that the Revolutionary Armed Forces of Colombia (FARC) was planning a major attack.