Ten soldiers have been killed and 20 injured in an apparent attack by leftist guerrillas in Colombia, a possible violation of the rebels' pledge of a unilateral ceasefire that could jeopardise the future of peace talks.

The attack occurred around midnight on Tuesday in the volatile southwest department of Cauca when an army unit on a routine patrol was surprised by guerrillas firing homemade explosives and grenades.

A non-commissioned officer and nine others were killed during the ambush by a unit of the Revolutionary Armed Forces of Colombia, or FARC, the army's third division said in a statement.

President Juan Manuel Santos offered his condolences to the victims' relatives and said he would travel to the combat zone on Wednesday to investigate the circumstances of the attack.

"This is precisely why we want to end the war," he said in a message posted on Twitter.

Al Jazeera's Alessandro Rampietti, reporting from the Colombian capital Bogota, said: "This is the deadliest attack since they [rebels] announced the unilateral indefinite ceasefire back in December. And comes just a few days since the Colombian government announced the extension of the suspension of the air raids over FARC camps.

"At this point it is not clear what kind of consequences [the attack] will have on the peace talks."

Colombians immediately took to social media to denounce the attack and call on Santos to abandon the peace talks, which have been making steady progress towards the goal of ending a half-century of fighting.

"Santos, don't betray us anymore," former President Alvaro Uribe, a fierce critic of the peace process, said on Twitter. "Don't justify the murder of our soldiers with this talk of war you want to end."

Peace talks

FARC negotiators in Cuba committed in December to a unilateral ceasefire to promote peace talks that have taken place on the communist-led island over the past two years, saying they would only fire weapons if attacked by the armed forces.

In a good faith gesture, the government responded by suspending all aerial attacks on guerrilla camps, a move that Santos reaffirmed this week.

But it is unclear how much control the leadership in Havana has over all of FARC's estimated 7,000 troops on the battlefield, especially in turbulent, lawless areas like Cauca, where rebel commanders are known to be heavily involved in drug-trafficking.

From Havana, the guerrilla commander known by the name Pastor Alape said he was unaware of the circumstances that led to Tuesday's combat.

The commander called on Santos to immediately declare a bilateral ceasefire, something the FARC has been urging since the start of negotiation, to prevent any further incidents that could obstruct the path to peace.

"It's urgent for the nation, something the entire country is waiting for," he said.

Source: Al Jazeera And AP