The kidnapped men were working for oil service companies Tuboscope and Tecnioriente, subcontracted by the local unit of US company Occidental Petroleum near the Caricare oilfield in Arauca state, a local army commander said, according to a Reuters report.

A sixth worker managed to flee into bushes when rebels, of the left-wing Revolutionary Armed Forces of Colombia (Farc) movement crashed their vehicle as army helicopters closed in on them on Saturday.

Violence and kidnappings in the country's long civil war have eased under President Alvaro Uribe, who sent troops to retake areas under rebel control. But the kidnappings underscored the threat guerrillas still present in the Andean country.

"They kidnapped six workers from Tuboscope and Tecnioriente," army commander General Rafael Neira told local radio. "They took them to a rural area ... the army reacted and rescued one of the workers."

Arauca state Governor Luis Ataya said he believed the men were taken for extortion and blamed Farc.

Once a powerful rebel force, Farc has been battered to its weakest in decades. Foreign investment, especially in oil and mining, is booming as companies are drawn to Colombia.

The country is now Latin America's four-biggest oil producer with output of more than 700,000 barrels per day.

Rebels have often snatched civilians for extortion, but they are also holding 24 soldiers and police for political leverage as part of Latin America's oldest insurgency.

Weakened by the loss of top commanders and desertions, Farc has turned to hit-and-run tactics, ambushes and home-made landmines to harry troops. But they can still carry out high-profile attacks.

In December a guerrilla commando unit snatched the Caqueta state governor from his home, speeding him into nearby jungles where they slit his throat and dumped his body.

The oil worker kidnapping came just days before the Farc planned to free two soldiers, one of them held for nearly 12 years in secret camps in the jungle. Brazilian helicopter crews and a Red Cross commission are standing by to pick them up.