The bodies of more than 30 people were found in a series of mass graves in a violent area of northeastern Colombia home to drug traffickers, far-right paramilitaries and leftist guerrillas.

Colombian investigators excavated 20 sites between April 2 and April 9 looking after residents reported 31 killings and 37 disappeared, the attorney general said in a statement Tuesday. Most of the villagers blamed a bloc of far-right paramilitaries that operated here until its demobilization in 2004, said the statement.

"More than 30 human remains have been handed over to be identified," Manuel Luna, secretary of interior for the province of Northern Santander, where the bodies were found, told RCN television.

Authorities said further analysis is required to establish exactly how many bodies are in the graves, their identities and when they were killed.

Colombia's four-decade civil war is one of the world's longest, and it kills thousands each year. The International Committee for the Red Cross says 3,600 people are recorded as disappeared.

Paramilitaries are in a peace process with the government that has seen more than 20,000 demobilize. Families of those disappeared are hoping that the demobilized fighters will provide information on other mass graves.