Four countries supporting peace talks between the Colombian government and FARC rebels called Tuesday for an "urgent de-escalation" of armed conflict in the South American nation.

The appeal comes after clashes resumed in mid-April, following an ambush by the Revolutionary Armed Forces of Colombia (FARC) that left 11 soldiers dead. Each side blames the other for the escalation.

Cuba and Norway are acting as so-called "guarantor" countries in the peace talks that began in November 2012. Chile and Venezuela are acting as "escort" countries.

"We urge the parties to strictly restrict any actions that cause victims or suffering in Colombia, and to step up the implementation of confidence-building measures," Norway representative Idun Aarak Tvedt said in a statement to journalists.

"We consider these steps to be essential in order to guarantee the conditions for and create a climate conducive to achieving agreement."

Despite the appeal two soldiers were killed, two wounded and a fifth reported missing in southern Colombia Tuesday following attacks that were believed to have been carried out by the FARC.

The group's chief negotiator, Ivan Marquez, welcomed the appeal.

He accused government forces of stepping up attacks on rebel camps while the guerrillas were observing a unilateral truce, which they ended in May after five months of relative calm.

Since then, about 30 rebels have been killed in army operations and recent surveys show the public to be wary about the peace process.

Colombia's civil strife dates back to 1964 and has drawn in left-wing guerrillas, right-wing paramilitaries and drug gangs, killing more than 220,000 people and uprooting as many as six million.

Despite the renewed bloodshed the Colombian government said for the first time Saturday that it was potentially open to a bilateral ceasefire.

So far, the two sides have agreed on three points of a six-point agenda for the peace process.