BOGOTA: The body of a kidnapped governor was found with his throat slashed, said Colombian President Alvaro Uribe hours after he launched a massive military operation to rescue the man from Marxist rebels.

"We still don't have the time of the murder, but we did confirm that his throat was slashed. The cowards slit his throat," Uribe said in a nationally broadcast speech.

"Military high command told me that as law enforcement was in hot pursuit, the terrorists, most likely to avoid firing shots, went ahead and slit the governor's throat," the president added.

Caqueta Governor Luis Francisco Cuellar's body was discovered by farmers near the charred remains of a car from which he was kidnapped on Monday, 15 kilometers (10 miles) south of southwestern Caqueta department capital Florencia.

The Revolutionary Armed Forces of Colombia (FARC), Latin America's oldest and longest-fighting rebel force, has stepped up its attacks lately despite Uribe's effort to defeat them. It holds captive hundreds of hostages, including soldiers and local officials.

A unit of the FARC on Monday lobbed a grenade at Cuellar's residence in Florencia and exchanged gunfire with security guards before kidnapping the governor and fleeing.

Interim Caqueta governor Olga Patricia Vega said that after the kidnap, Cuellar apparently had trouble walking which led to his execution by his captors.

Vega said Cuellar, who turned 69 on Tuesday, had already been kidnapped four times before he became governor.

Uribe slammed the FARC for offering to release two captive soldiers at the same time they were kidnapping Cuellar.

"We can't understand why this terrorist group performs these theatrics... and while the government offers every guarantee, this FARC group responds by not releasing (the soldiers) and instead goes ahead and murders the governor."

"The armed forces must defeat these kidnappers," Uribe said, promising to "forge ahead until terrorism is fully defeated."

Uribe earlier Tuesday announced a "full military and police rescue operation" to find Cuellar and 24 troops held by FARC rebels.

The United Nations' Office of the High Commissioner of Human Rights in Bogota issued a statement condemning Cuellar's kidnapping and murder and called on FARC to "immediately and unconditionally set free all the captives it is holding."

Uribe has rejected a political dialogue with the FARC, which is seeking a prisoner swap with the government to exchange its hostages for 500 FARC rebels in government jails.

Last year some of the FARC's most high-profile hostages were rescued from their jungle captivity, including French-Colombian politician Ingrid Betancourt and three Americans.