Bodies may have been moved from mass graves in Kenya to prevent an investigation into a suspected slaughter of villagers during inter-tribal unrest in the Tana River region, police said.
The suspected graves were found on Monday in Kilelengwani village, the focus of fighting in the coastal area that has killed more than 100 people in the past three weeks, including nine police officers.
The scale of the unrest has left many Kenyans convinced it was politically instigated and has raised fears of serious tribal fighting before elections due in March.
The Kenya Red Cross said at least 20 people believed to have been killed were still unaccounted for, and they suspected their bodies had been buried in the graves. Regional police chief Aggrey Adoli said only a human foot and human skin had been found after two hours of digging, however.
"The whole place appeared freshly dug and was exuding the stench of rotten flesh ... we all were surprised when nothing was found. Those who removed the bodies must have been striving to hide some evidence," he said by telephone late on Thursday.
"It is possible that the graves might have been tampered with and bodies removed before police arrived at the scene to seal it off," Adoli said.
Raiders shot, hacked and burnt to death 38 people last week in Kilelengwani and 20 people have been arrested and charged with murder over the killings. Those arrested include members of both rival tribes involved in clashes, the Pokomo and Orma.
Local human rights groups have blamed the violence on incitement by politicians seeking to drive away elements of the local population they believe will vote for their opponents.
President Mwai Kibaki imposed a curfew last week and sent extra security forces to the area to try to end the violence, intensified by an influx of weapons in the last few years.
Settled Pokomo farmers and semi-nomadic Orma tribesmen have clashed for years over access to grazing, farmland and water in the coastal region. Dams along the Tana River, Kenya's longest, supply about two thirds of the east African state's electricity.