The left-wing rebel group in Colombia, known as FARC, announced one of their peace negotiators was among the 27 rebels who were killed last week in a military raid.

The Revolutionary Armed Forces of Colombia (FARC) released a statement saying that the Jairo Martinez died on May 21 in an air strike conducted by the Colombian government that targeted a rebel camp in the country's southwestern Cauca province. Forensic analysis identified the insurgent as Jairo Martinez, although his real name was Pedro Nel Daza, reports The Guardian.

The former envoy to the government had joined the FARC negotiating team in February 2014. According to FARC, Martinez participated in peace talks aimed at putting an end to the country's five-decade civil war. FARC says the air and ground attacks came when the 63-year-old veteran fighter was on an "educational mission" to discuss progress in the peace process, reports BBC News.

Although the FARC fighters and Colombian government are engaged in peace negotiations, they have yet to sign a ceasefire. President Juan Manuel Santos has also refrained from commenting on Martinez's death.

"The government has to explain why a person involved in the peace process has ended up dead in a military action," Sen. Ivan Cepeda of the leftist Alternative Democratic Pole party told The Associated Press.

Since the raid, the FARC has hardened its position while negotiators in Havana decided to lift a unilateral cease fire in place since December.

Following the raid, representatives of the guarantor nations at the Havana peace talks, Norway and Cuba, expressed concern on Wednesday about the "escalation of the armed conflict in Colombia." They also called for a cease-fire on both sides.

Dag Nylander of Norway and Rodolfo Benitez of Cuba released a statement saying that tensions from the recent bloodshed "undermine confidence gained in the two years of negotiations."