Assailants in pickup trucks fired homemade mortars at a police station in this western town Thursday, killing at least six people and wounding more than 20, the regional police chief said.
The Cauca state police chief, Col. Ricardo Alarcon, said it was too early to assign blame.
But President Juan Manuel Santos and his defense minister both said they had no doubt the authors were the leftist Revolutionary Armed Forces of Colombia, or FARC, the country's main insurgency.
The 1 p.m. attack in this town of 15,000 people about 15 miles (25 kilometers) southeast of Cali, the country's third-largest city, came a day after a bomb planted in a tricycle killed nine people and wounded 76 outside a police station in the Pacific port of Tumaco as lunch hour was ending.
FARC rebels are active in both areas and their arsenals include homemade mortars. Defense Minister Juan Carlos Pinzon blamed Wednesday's attack on the insurgents in league with a drug-trafficking gang.
"What is the FARC looking for?" Santos said as he toured Tumaco on Thursday. "Why do they speak in the language of peace but on the other hand commit acts of terrorism like this?"
The peasant-based FARC, which has been fighting a succession of governments since 1964 demanding a more equitable distribution of wealth, is seeking to open a peace dialogue with Santos.
But Santos insists the rebels must first halt hostilities and release 12 security force members who the insurgents have held captive for more than a decade.
The dead in Thursday's attack included the Villa Rica police post's commander and five civilians, Alarcon said. He said 35 officers were in the police station when at least three mortars were fired at it from a moving pickup truck about 150 feet (50 meters) away.
Among the dead were 3-year-old girl and a 19-year-old woman, state health chief Oscar Ospina said. He said the wounded had to be evacuated from Villa Rica because its hospital is next to the police station and was damaged in the attack.
This week's attacks were the most serious affecting civilians since a car bomb killed six people and wounded more than 30 in March 2010 in the Pacific port of Buenaventura.
Like Tumaco, Buenaventura has long been a hub for cocaine smugglers, who include leftist rebels and far-right militias.
The region where Thursday's attack occurred is a key corridor for cocaine-smuggling to the Pacific coast. Its craggy mountains and steep valleys were also where FARC's commander, Alfonso Cano, roamed before he was killed by government troops in November.
The FARC numbers about 9,000 combatants. Although it has suffered major setbacks in recent years, analysts say its hit-and-run attacks have been rising. In January alone, it staged 133 attacks on police and military targets, according to the independent think tank Nuevo Arco Iris.
The main FARC analyst for Nuevo Arco Iris, Ariel Avila, said the rebels are seeking "to show themselves stronger in order to put on pressure for a peace dialogue."
Another security analyst, Alfredo Rangel, said last month saw the most FARC attacks in a single month since January 2004, when there were 45.
Associated Press writers Vivian Sequera, Cesar Garcia and Libardo Cardona in Bogota, Colombia, contributed to this report.