Armed groups in Colombia are driving peasants off their land to make way for plantations of palm oil, a biofuel that is being promoted as an environmentally friendly source of energy.

Surging demand for "green" fuel has prompted rightwing paramilitaries to seize swaths of territory, according to activists and farmers. Thousands of families are believed to have fled a campaign of killing and intimidation, swelling Colombia's population of 3 million displaced people and adding to one of the world's worst refugee crises after Darfur and Congo.

Article continues Several companies were collaborating by falsifying deeds to claim ownership of the land, said Andres Castro, the general secretary of Fedepalma, the national federation of palm oil producers.

"As a consequence of the development of palm by secretive business practices and the use of threats, people have been displaced and [the businesses] have claimed land for themselves," he said. His claim was backed up by witnesses and groups such as Christian Aid and the National Indigenous Organisation of Colombia.

The revelations tarnish what has been considered an economic and environmental success story. The fruit of the palm oil tree produces a vegetable oil also used in cooking, employs 80,000 people, and is increasingly being turned into biofuel.