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BOGOTA, June 24 (Reuters) - A man and a 3-year-old girl were killed on Sunday when guerrillas detonated a bomb at a tourist beach in Colombia's main port city, where rebels have been blamed for several attacks over the last two days, authorities said.

Officials said the Revolutionary Armed Forces of Colombia, or FARC, detonated a bomb as a tractor passed through a beach area on the outskirts of Buenaventura, killing the man and the girl and wounding seven others.

On Friday and Saturday, seven bombs or grenades exploded at a police station and commercial centers, injuring 23 people in the Pacific port city that handles about half of the Andean country's international shipments.

"This is retaliation from the FARC for the killing of one of their key leaders," Interior Minister Carlos Holguin told local Caracol Radio. "These bandits have decided to attack the civilian population and create acts of terror."

Local television reported the bomb may have been intended for a passing police patrol. But tourists fled the beach after the attack, which damaged nearby buildings and left a crater in the road.

Colombia remains the world's biggest producer of cocaine despite billions in U.S. military and counternarcotics aid to fight guerrillas who use drug trafficking and extortion to finance Latin America's oldest insurgency.

Violence from the conflict has dropped under Colombian President Alvaro Uribe, but the FARC, a smaller rebel group known as the ELN, and renegade paramilitaries still fight in remote parts, often over the spoils of the drug trade.

The FARC began as a peasant army in the 1960s fighting for a socialist state. Uribe's U.S.-backed campaign has driven the rebels back into the jungles and urban bombings are now rare.

But Buenaventura, with its easy access to the coast, has become embroiled in a battle among urban guerrilla groups, drug traffickers and paramilitary gangs for control of lucrative narcotics smuggling routes.

Experts say Colombia produces around 600 to 700 tonnes of cocaine a year, most of its destined for the United States and Europe.

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