President Juan Manuel Santos Friday vowed to step up a military crackdown on leftist rebels after they killed 14 police officers and three soldiers since he took office on August 7.

"The order I've given military and police commanders is to get tough, get tough, get tough!" Santos said after a cabinet meeting.

"We can't let our guard down. We must confront terrorism with everything we've got," he added, vowing to continue the crackdown on insurgents his predecessor Alvaro Uribe launched in 2002 and which he spearheaded as Uribe's defense minister from 2006-2009.

Santos, 59, spoke in southern Caquete department, where the latest rebel attack on Wednesday took the lives of 14 police officers when their patrol vehicle was blown up by a land mine.

The bombing was blamed on the Revolutionary Armed Forces of Colombia (FARC), the country's oldest and strongest rebel group that has offered talks with the government, which Uribe and now Santos have conditioned on an end to their violence.

Santos on Friday reiterated that the door to negotiations "is not closed" as long as the rebels release all their hostages -- some of them held more than 10 years -- and stopped pressing children into their ranks.

Three soldiers were killed and seven were wounded Thursday in two battles with FARC guerrillas in Norte de Santander and Narino departments, on the borders with Venezuela and Ecuador respectively.

Santos met in Caqueta with the country's top generals to review anti-rebel strategy in the southern department FARC has made its stronghold.

Interior Minister German Vargas warned the FARC that Wednesday's police massacre was considered a "crime against humanity" by the government and that such actions "will never benefit from an amnesty or a pardon."

The government has offered a 500 million peso (275,000 dollars) reward for information leading to the capture of the FARC commander suspected of masterminding the Caqueta bombing, known by his nickname Wilmer.

Colombia's crackdown on guerrillas Friday killed 15 members of the leftist National Liberation Army -- the country's second-largest rebel group -- during an Air Force bombing raid in eastern Arauca department bordering Venezuela, officials said.