Only about 42 percent of the criminal activities of these gangs are related to drug trafficking, the organisation said.

'The other 58 percent has to do with extortion, stealing land and the most serious, common crime in the streets of the big cities,' it said.

Fundacion Nuevo Arco Iris said it determined that the emerging paramilitary groups have a total of 10,000 fighters in their ranks, 'of whom 5,000 are demobilized (militiamen) who have returned to crime'.

The United Self-Defense Forces of Colombia, or AUC, accused of committing numerous human rights violations, demobilized more than 31,000 of its fighters between the end of 2003 and mid-2006 as part of the peace process with President Alvaro Uribe's administration.