A United Nations team has started investigating three mass graves found in the Democratic Republic of Congo.
The DR Congo saw incursions by Rwandan troops in 1996
Dozens of skulls and bones have been exhumed from the graves, discovered at Rutshuru, about 50km (30 miles) north of Goma more than a week ago.
They are the latest in a number of mass graves found in the region recently.
A UN spokeswoman told the BBC the remains were believed to be those of Congolese and Rwandan Hutus killed by Rwandan soldiers in 1996.
At the time the Rwandan Army was venturing into the DR Congo trying to find those responsible for mass genocide in Rwanda in 1994.
The graves were exhumed by Congolese troops.
"They are Congolese Hutus who were massacred by the Rwandan army in 1996 and in the following years," the commander of the troops, Col Jean-Marie Shekasikila, said.
Following the 1994 genocide, which saw more than 800,000 Tutsis and moderate Hutus killed, many Rwandan Hutus fled to neighbouring DR Congo fearing for reprisals from the new-Tutsi-led government.
Hutu extremists who are thought to have helped carry out the killings also crossed the border to set up camps. Some 15,000 are still thought to be in the country.
The resource-rich country has been in turmoil for years
We believe that thousands of people were massacred and that we will discover more graves," said Colonel Shekasikila of the 5th Brigade, who are carrying out the diggings..
"We found the first one as we were doing digging work to build a latrine, then town residents showed us two other spots where there were bones," he said.
Captain Jose Mabiala, a spokesman for the 5th Brigade, accused Rwandan officers of being responsible for the killings.
"Rebels backed by Rwanda dominated the Rutshuru region at the time and young army officers came to kill residents," he said.
The country, one of Africa's most resource-rich states, was in political turmoil at the time, which eventually led to the overthrow of its dictator Mobutu Sese Seko.
UN troops continue to keep the peace in the country, which threatens to erupt into civil war.