In a report released Tuesday, New York's Human Rights Watch said at least 18 civilians died in the fighting in mid-May. The group says most of the dead were deliberately killed by Sudanese Armed Forces or by government aligned militias.

"Two months after the clashes there is still no clear information on how many civilians died and under what circumstances," said Georgette Gagnon, Africa director at Human Rights Watch. "Without a full and independent investigation, accountability for the killings, looting, and massive destruction in Abyei will not be possible."

Human Rights Watch said an investigation into the massacre has not been possible since the Sudanese military has restricted access to the town.