A human rights group has called on Kenya to account for at least 300 people who disappeared as authorities cracked down on insurgents in the Mount Elgon region three years ago.

U.S.-based Human Rights Watch is calling for an independent investigation of suspected mass graves and of atrocities allegedly committed by Kenyan security forces and the rebel militia known as Sabaot Land Defense Force (SLDF).

The rights group said the International Criminal Court should step in to conduct the probe if the Kenyan government fails to do so.

In a 48-page report released Thursday, Human Rights Watch said the government's failure to conduct credible investigations has left relatives of the missing in a “legal and psychological limbo.”

In 2008, the Kenyan military launched a five-month operation against the SLDF, which claimed to be fighting for local land rights.

Rights groups have alleged the SLDF abducted, tortured and killed civilians who did not follow the group's orders. They also have accused Kenyan forces of rounding up nearly all men in Mount Elgon, and torturing and killing many of them during interrogations at military camps.

Human Rights Watch said between 2006 and mid-2008, the SLDF killed about 750 people and Kenyan security forces killed an estimated 270.

Additionally, the group says, more than 300 involuntarily disappeared, about 200 of them at the hands of security forces.

HRW said its report is based on information gathered during field investigations and interviews in the western Kenyan region.