I hope the FARC recognises that it is its failure to negotiate in seriousness that has caused this crisis to come about

US Secretary of State Colin Powell

Colombian tanks and troops have already begun moving towards the rebel-controlled demilitarised zone in the south of the country in readiness to drive the FARC fighters back into the jungle.

If there is still no agreement by Saturday, the rebels will have a further 48 hours in which to leave the safe haven.

A statement from the rebels said they were still open to a negotiated way out of the crisis - but offered no new concessions.

Click here for a map of the FARC's safe haven

Top army commanders met on Thursday to discuss their plans to deploy at least 13,000 soldiers in preparation of a presidential order to retake the demilitarised zone.

Military officials said rapid deployment troops and counter-guerrilla forces were preparing to retake the enclave's five major towns, and push the rebels into the jungle.

Earlier, US Secretary of State Colin Powell expressed his support for Mr Pastrana's decision to suspend the peace talks, blaming the rebels for their failure.

Last chance for peace

Colombia's government and the FARC were earlier urged to resume peace talks by 10 countries which have been backing the four-year-old peace process.

Everyone is afraid, but we are staying put. We have been here forever

FARC fighter Eliana Gonzales

Daniel Parfait, France's ambassador to Colombia, called on both sides "to come back to the negotiating table".

Bogota has given the 16,000-strong Revolutionary Armed Forces of Colombia (FARC) until Friday night to leave the demilitarised area roughly the size of Switzerland

The area, which has in effect been run by the rebels as their own Marxist state, was ceded to them in 1998 to kick-start the talks.

President Andres Pastrana announced the end of the peace process in a nationally broadcast address to the nation on Wednesday night.

Many guerrillas have already left the enclave's main town, San Vicente, melting into the nearby jungle.

Pastrana has often swallowed his pride to deal with FARC

Eliana Gonzales, a 45-year-old member of a FARC force who remained, told Reuters that she was ready to fight.

"Everyone is afraid, but we are staying put. We have been here forever," she said, gripping her AK-47 assault rifle.

People in San Vicente, where camouflage-clad FARC guerrillas have long been a common sight patrolling with machine guns or loitering about, said they feared what might come next.

"To the army, we are all potential guerrillas, because we live here. And to the guerrillas, once the army gets here, we are fair targets," said one 21-year-old resident quoted by Reuters.

Doors open

The peace process to end nearly four decades of war was started by President Pastrana, who has since dedicated much of his time in office to the job.

After three years of talks, the two sides have never reached a single agreement on a peace treaty, but correspondents say few people thought Mr Pastrana would abandon the negotiations so close to leaving office in August, after the next presidential elections.

Mr Pastrana has frequently bowed to the rebels' demands and renewed their rights to the enclave, even after high profile killings - including the murder in September of the attorney general's wife and recent kidnappings of congressmen.

In his address on Wednesday, Mr Pastrana said the search for peace had not ended.

"I will maintain the doors of dialogue and negotiation open," he said.