Pastrana says the church attack was a "genocide"

The Marxist rebels say they hit the church by mistake during a battle with the United Self-Defence Forces of Colombia (AUC), a right-wing paramilitary group.

Mr Pastrana pledged to rebuild the church after walking through its ruins.

He also met survivors of the fighting.

"We are here because a massacre was committed that should be condemned by the entire world," Mr Pastrana said.

"We are here to share their pain."

Government criticised

Some residents in the region have accused Mr Pastrana of abandoning them to the fighting.

And the government's own human-rights ombudsman, Eduardo Cifuentes, has criticised Bogota for failing to prevent the most recent killings.

It is alleged the army was warned as long ago as last June that such an attack might occur, but troops were never deployed to the area.

Government troops only secured the remote region on Wednesday, finding what was left of the church and the scattered remains of those who died inside.

The president promised on Thursday that a military gunboat would make regular patrols of the nearby Atrato River to better protect local people.

He was accompanied to the isolated north-western village by government ministers and a high-level delegation from the United Nations, which is conducting a fact-finding mission.

The FARC and the AUC had been battling to control the Atrato - a main conduit to the Caribbean Sea and neighbouring Panama and a lucrative arms and drugs-smuggling route.

Civilians fleeing

Colombian authorities say thousands of civilians have fled the area.

On 1 May, the FARC attacked a boat carrying AUC fighters, triggering fierce clashes between the two sides.

The church was hit as AUC fighters reportedly took up positions in the village.

The AUC was believed to have had the tacit support of the Colombian armed forces.

But last week, the United States said the Colombian army had severed links with the AUC, making it eligible for more US aid.