Alvaro Uribe, Colombia's president, said that the deaths of the government troops in the southwest, which contains several key drug-smuggling routes used by the Farc, were a tragedy.

'Retreat from attack'

A Colombian soldier who was among those who came under attack by the Farc fighters, said that he had been forced to pull back from the fighting after being overwhelmed by the ferocity of the onslaught.

"I fired three or four magazines and had to retreat," the solider told local television.

"I saw that my friends were dying. Most of them had been hit by home-made grenades."

Uribe's US-backed military campaign has failed to eliminate Farc's influence [EPA]
The incident in Corinto shows that the Farc still has the capacity to launch major attacks despite Uribe's US-backed military campaign aimed at destroying the group.

While many cities across Colombia have experienced fewer outbreaks of violence by the Farc since Uribe came to power in 2002, the group still has a firm hold in the countryside and has continued to profit from the illegal drugs trade.

Cocaine produced in southern Colombia's dense jungle territory is sent from Cauca to the Pacific coast, where it is then shipped to the US.

Uribe is thought to be considering running for a third term as president if his political allies win enough support for changes to the constitution that would enable him to stand in elections scheduled for May.

The constitution was changed to allow Uribe to win a second term in 2006. Farc fighters usually carry out attacks with a greater frequency in the months before elections.

"There has been a reactivation of the Farc in recent months in places like Cauca and Norte de Santander, near the Venezuelan border," Mauricio Romero, a political science professor at Bogota's Javeriana University, said.

"The Farc no longer presents a strategic threat to the state, but they are making the point that they can still do damage despite Uribe's counter-offensive," he said.