BOGOTA, Nov 20 (Reuters) - A provincial Colombian governor escaped unharmed but a soldier was killed when guerrillas detonated a bomb outside the politician's residence in Cauca late on Monday in a rare urban attack, authorities said.

Four soldiers were wounded and two rebels killed in combat when troops discovered the bombers outside the residential complex in Cauca, a strategic region for drug and arms smuggling to the Pacific coast and close to Ecuador's border.

Authorities blamed the bombing on the Revolutionary Armed Forces of Colombia, known as the FARC, which is fighting Latin America's oldest insurgency and is now engaged in cocaine trafficking trade to finance its operations.

"We felt the house move. We were told they placed an explosive outside and had planned to set it off when I left," Gov. Juan Jose Chaux told local radio.

Violence from the four-decade conflict has ebbed as President Alvaro Uribe pushes a U.S.-financed campaign to drive guerrillas back into rural areas and retake towns and highways once dominated by armed groups.

Bomb experts on Tuesday deactivated three other explosives packed into milk churns and buried near the entrance of the governor's residence on the outskirts of Popayan city, about 394 miles (633 km) south of the capital.

The guerrillas remain potent in some remote areas, especially in southern provinces such as Cauca where terrain impedes military operations and where coca leaf is cultivated to make cocaine for U.S. and European markets.

Earlier this year, guerrillas tried to bomb the mayor of Neiva city in neighboring Huila province. She survived the attack when a bodyguard spotted the suspicious vehicle but five people died when another bomb exploded two days later. (Reporting by Patrick Markey in Bogota; Editing by Bill Trott)

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