A law supposed to help Colombian families displaced in the country's armed conflict risks failing millions of people, according to a report by Amnesty International.

In effect since 2012, the so-called Victims and Land Restitution Law was designed to help return illegally acquired land to some of its rightful occupants.

"However, only a tiny percentage of the millions of hectares stolen has been returned," Amnesty wrote in a statement Wednesday announcing the publication of its report, "A land title is not enough."

Nearly six million people -- about 13 percent of the population -- have been forcibly displaced since 1985, Amnesty said, most of them because of Colombia's five decades of armed conflict.

"There is a risk of failure of land restitution to millions," Amnesty spokesman Esteban Beltran told AFP.

"Out of eight million hectares that were abandoned or stolen during the conflict, fewer than 30,000 have been returned," he added.

According to official figures, Colombia's internal conflict has left 220,000 dead and displaced 5.3 million people over the past 50 years.

Compiled over a two-year period, the report found that land claimants, human rights activists and officials have been threatened and killed, mostly by paramilitaries.

"Impunity is rife," Amnesty said. "The majority of those suspected of having criminal responsibility for forced displacement and related human rights abuses have never been brought to justice."

The rights group also criticized the fact the law only potentially helps people impacted after 1991, and is only in effect for 10 years -- three years of which have already passed.

The issue of land is central to the conflict in Colombia, which since the 1960s has seen rebel groups such as the Revolutionary Armed Forces of Colombia (FARC) fight government forces.

The FARC and the government have been involved in lengthy peace talks in Cuba, which are currently suspended.