Red Cross officials say they have reports that about 70 police and 10 civilians were killed during the raid on the station at Mitu near the Brazilian border.

Correspondent Quill Lawrence says raid has made communications with town impossible

They say they fear another 40 police were abducted when rebels from the Revolutionary Armed Forces of Colombia (FARC) overran the base.

According to reports, the rebels attacked the base using rudimentary missiles made from modified propane gas cylinders.

President Andres Pastrana cut short a visit to Venezuela as news of the guerrilla offensive developed.

The Colombian army says it has sent in large reinforcements to the base in a remote eastern part of the country. Impact on peace talks

Our correspondent in Bogota, Quill Lawrence, says planned peace talks between the government and the rebels may be delayed as a result of the attack.

FARC rebels control around a third of the country's territory

When he took office three months ago, President Pastrana vowed to make peace his top priority. He issued a decree recognising the political status of the rebels in an effort to entice them to the negotiating table.

The government is currently completing a pullout of all soldiers and police from more than 40,000 square kilometres of jungle in the south of the country, which FARC has demanded as a safe zone.

The demilitarisation is due to be completed by Saturday, and formal talks may begin any time within the 90 days of the troop withdrawal.

But FARC has insisted that negotiations must go on in the "middle of the war".

They have said that they will not lay down their weapons or demobilise before or after any peace deal and aim to win at least a part-share of national power.

To complicate matters further, right-wing paramilitary forces who work alongside the army have announced their intention to enter the negotiation zone and kill civilians whom they suspect of supporting the rebels.

Drug funds

Our correspondent says the region where the attack occurred is known for the cultivation of coca, the plant used to make cocaine, which the guerrillas tax heavily to fund their war.

FARC is the country's oldest and largest rebel group. They have been waging a war for 40 years, and are estimated to control more than one-third of the national territory.

The Marxist group is demanding an end to free market economics and sweeping land reform.

More than 35,000 people have died in the last ten years of Colombia's long-running civil war.