Colombian honour guards carry the coffins of four members of the security forces during their funeral at Bogota's cathedral.

Bogota - Colombia vowed on Tuesday to keep searching for captives of FARC guerrillas despite pleas from families to avoid putting their loved ones at risk after the rebels executed four hostages during a military raid.

Three policemen and a soldier held captive for more than a decade were shot dead by FARC insurgents at the weekend during a firefight. It was the most violent act by the group since troops killed its leader Alfonso Cano earlier this month.

Three were shot in the head, the fourth in his back. Human rights group called the killings a war crime.

With police and soldiers guarding them, President Juan Manuel Santos, the military high command and ministers joined families in Bogota's main cathedral to mourn the four.

Asked if Colombia would continue the hunt for hostages, Defense Minster Juan Carlos Pinzon said: “It's a duty of the security forces to always be ready to protect the life, rights and liberty of citizens so it will always be necessary to act with that objective.”

At least 11 police and soldiers are still being held by the Revolutionary Armed Forces of Colombia (FARC). Families have traditionally opposed military operations to free captives given the risks facing hostages during rescue attempts.

In a letter supposedly sent before the military operation at the weekend, the FARC's seven-member ruling secretariat said it had taken the decision to free six hostages as a “humanitarian act,” though it did not specify which captives.

The letter - addressed to activists and former Senator Piedad Cordoba - was published on Tuesday on, a website that routinely carries FARC statements. Cordoba said the note was sent before the military strike.

Later on Tuesday, the FARC said that the four dead hostages and one who escaped during the battle with troops over the weekend had been taken to the area to be eventually released.

“We inform the nation and the world that this deed was due to the eagerness of President Santos and the military high command to prevent the imminent, unilateral release,” it said in a statement posted on a news website called the Bolivarian Press Agency that regularly carries FARC communiques.

Kidnapping has been the scourge of Colombia for decades. Only a few years ago rebels were able take scores hostage at a time when attacking military bases and cities, or snatch people off the main roads across the Andean country.

But a US-funded crackdown against leftist rebels since 2002 has pushed them to ever remoter jungle and mountain hide-outs. Better intelligence and mobility has given Colombian forces the ability to deal heavy blows to guerrillas.

The major advances Colombia has made on security, however, mask deep-seated problems from land rights and rural poverty to government corruption and the influence of drug gangs.

Some of those issues date back to the formative years of many FARC leaders when the country emerged from the political violence of the late 1940s and 1950s that killed hundreds of thousands and power was concentrated in only two parties.

Almost every government since the 1980s has tried peace talks with illegal armed groups with varying degrees of success, but the conflict with the FARC and a smaller rebel group has proved the most intractable.

The killing of the four hostages is likely to dampen any talk of peace for a while - Santos had said the door to peace was not closed if rebels agreed to demobilise and release captives, but that was rejected by the FARC.

“It's sad and terrible that they waited so many years and the FARC killed them. It makes me ashamed that this happens in my country,” said Marisa Moreno, a university student, as she waited outside a trendy Bogota restaurant.

“There'll never be peace with these people. They only want war.” - Reuters