GENEVA - A top U.N. human rights investigator Friday released a scathing report that blames the Sudanese government for atrocities against its civilians in the Darfur region and says "millions of civilians" could die.

"It is beyond doubt that the Government of the Sudan is responsible for extrajudicial and summary executions of large numbers of people over the last several months in the Darfur region, as well as in the Shilook Kingdom in Upper Nile State," said Asma Jahangir, the U.N. investigator on executions, in a report based on a 13-day visit to the region in June.

"The current humanitarian disaster unfolding in Darfur, for which the government is largely responsible, has put millions of civilians at risk, and it is very likely that many will die in the months to come as a result of starvation and disease," said Jahangir, a Pakistani lawyer.

Jahangir said there was "overwhelming evidence" that the killing was carried out "in a coordinated manner by the armed forces of the government and government-backed militias. They appear to be carried out in a systematic manner."

The scale of violations means they "could constitute crimes against humanity for which the government of the Sudan must bear responsibility," she said in the 26-page report to the U.N. Human Rights Commission.

A leading U.S. lawmaker toured camps in eastern Chad holding hundreds of thousands of refugees and said he would investigate the relationship between the Sudan government and the militias. Senate Majority Leader Bill Frist also said the threat of U.N. sanctions against Sudan was not enough to end the violence.

The Tennessee Republican said he planned to talk with other U.S. lawmakers about remedying that, but he did not elaborate...