BOGOTA, Colombia (AP) _ As Colombian government troops sought to retake a besieged frontier town, the Red Cross said Monday that 60 police and 10 civilians were killed when guerrillas overran a police post over the weekend.

An estimated 800 leftist guerrillas, firing homemade missiles from modified propane gas cylinders, waged a 12-hour assault Sunday. The Red Cross said the rebels also took 40 police prisoner.

The assault in Mitu, the remote capital of southeastern Vaupes state near the border with Brazil, appeared to underscore the guerrillas' growing military might ahead of peace talks with President Andres Pastrana to end Colombia's 34-year civil war.

The Red Cross said the police barracks and a nearby farmers' bank had been burned to the ground as a result of the shelling from the makeshift missiles.

``It's difficult to get an exact count (of the dead)'' Red Cross spokesman Walter Cotte told The Associated Press.

Pastrana has promised to withdraw all troops from a large southern region by Saturday to allow peace talks with the Revolutionary Armed Forces of Colombia, whose guerrillas have been piling up victories against ineffective and dispirited army troops.

The president, who was headed back to Bogota Monday evening after cutting short a state visit to Venezuela, had yet to make any statements about the rebel attack.

His peace envoy condemned the attack, but insisted that Pastrana still planned to personally attend the opening of the peace talks, planned for the coming weeks in the 16,200 square-mile area where the army is pulling out.

``It's regrettable that at a time when we're promoting peace these kinds of actions occur, because instead of acts of war, what Colombia needs are acts of peace,'' the envoy, Victor G. Ricardo, said in a television interview.

Including the police taken in the weekend attack, the rebels now hold about 290 police and soldiers seized in battles during the past two years.

Pastrana has so far refused a guerrilla proposal to exchange the captives for 452 jailed rebels before peace talks begin.

The 200 troops advancing Monday toward Mitu were dropped by helicopter about 6 miles from the town of 15,000 inhabitants, police said.

Skirmishes between government forces and rebels began Monday afternoon near Mitu, Gen. Freddy Padilla of the Army's Seventh Brigade said in a radio interview.

Radio reports said 28 more police and soldiers were killed Monday in a rebel ambush. Police Gen. Leonardo Gallego said he could not confirm the report.

The jungle town _ normally accessible only by air and water _ was cut off from communications when the rebels seized control of the airport and blew up the phone company's microwave tower.

The guerrillas have not commented on the attack, which would be the largest since an August offensive where 143 police and soldiers were killed and 130 taken prisoner.