Colombian President Juan Manuel Santos said Wednesday that the "vile" attack by the Revolutionary Armed Forces of Colombia (FARC) would "not go unpunished."

"I have ordered the armed forces to lift the suspension of air strikes on FARC positions until further notice," Santos said.

Colombia's government stopped the bombing raids last month, after the FARC in December declared it was implementing a unilateral ceasefire.

The two sides have been taking part in peace talks in Cuba since 2012.

The overnight ambush, in which 10 soldiers and one rebel were killed, is the biggest violation of the ceasefire so far. At least nine government troops were also injured in the confrontation, which took place in the country's volatile southwest.

"This incident was a product of a deliberate attack by the FARC, it was not a coincidence and this implies a clear rupture of the promise of a unilateral ceasefire," Santos said.

FARC leader Pablo Catatumbo told Reuters the group regretted the events, which were not "premeditated."

The Marxist guerillas have repeatedly called for a bilateral ceasefire, but the Santos government has refused to end military action until a final peace deal has been agreed to.

Santos said the latest clashes indicated just how important it was to accelerate the peace process and put an end to the conflict.

"Let this be clear to the FARC: I'm not going to be pressured... by vile acts like this to make a decision on a bilateral ceasefire."

The five-decade conflict between FARC and the Colombian government has left 220,000 dead and displaced close to 5 million.

nm/bw (Reuters, AFP, AP, dpa)