Rights organisations on Tuesday called on the International Criminal Court to probe extra-judicial killings in Colombia, saying citizens were killed by the army and then passed-off as rebels.

The International Federation of Human Rights as well as the Colombia, Europe US Coordination "call on the ICC to open an investigation into crimes against humanity in Colombia" committed between 2002 and 2008, they said in a statement issued in The Hague.

The two non-governmental organisations on Tuesday released a report entitled: "Colombia: a war measured in litres of blood" in which they alleged the "systematic and widespread" extra-judicial executions of around 3,000 Colombian civilians.

The victims were then "presented as guerrillas killed in combat", the report said, adding it was done to boost claims of success by the army in operations against Colombia's rebel and militia movements.

"Such acts were supported by the highest military officials, who not only failed to exercise their duty to monitor, but also encouraged this behaviour," the two organisations said.

Colombia has been locked for almost half-a-century in armed conflict involving its army, left-wing guerrillas and right-wing militias.

ICC chief prosecutor Luis Moreno-Ocampo's office announced in 2006 that a preliminary examination into Colombia's violent struggle between its military, guerrillas and paramilitary forces had been launched.

Its aim was to check whether a full-blown ICC investigation was justified as a result of Colombian courts being unable or unwilling to try crimes against humanity, war crimes and genocide that may have been committed in the South American country.

"The FIDH and CCEEU reported structural flaws in investigations and trials held in Colombia because there are no procedures against senior military officials responsible for extra-judicial killings," the two NGOs pointed out.

The FIDH also said a confidential list of the main alleged perpetrators had been sent to the prosecutor's office.