Colombia's main rebel group said it is abandoning the practice of kidnapping and will soon free its last remaining "prisoners of war" - 10 security force members held for as long as 14 years.

The leftist Revolutionary Armed Forces of Colombia, or FARC, announced on its website that it would no longer kidnap civilians "for financial ends", unequivocally renouncing for the first time a tool it long used against Colombia's well-heeled as well as foreigners.

It is not clear whether an order has been given to release ransom-kidnapping victims currently held by the rebels, whose number is not known. Nor is it clear, given the insurgency's decentralised nature, whether the FARC's ruling seven-man secretariat can enforce its order.

The rebels are known to currently hold four foreigners, all Chinese oil workers abducted last June.

The FARC statement said kidnapping of civilians for ransom had helped sustain the insurgency, but added: "From this day on we are halting the practice in our revolutionary activity."

It did not provide a date for the release of the 10 security force members, two fewer than the government has said the insurgents hold.

The announcement could advance prospects for a peace dialogue sought by the rebels. The government has insisted the FARC end all kidnappings as a minimal first step.

The rebels did not say, however, that they were abandoning hostilities. They have recently stepped up hit-and-run attacks and the military blames them for a bombing and mortar attack on two police posts in the past month that killed 15 people and wounded nearly 100, most of them civilians.

President Juan Manuel Santos responded to the FARC announcement positively but cautiously via Twitter. He called it "an important and necessary, if insufficient, step in the right direction".

Alvaro Uribe, president in 2002-10, called it "deceitful" in a tweet.