UNITED NATIONS (Reuters) - The United States and other world powers should impose sanctions on key members of the Sudanese government for refusing to end violence in Darfur and south Sudan, a report by an anti-genocide group said on Monday.

Sudan's U.N. Ambassador Abdalmahmoud Abdalhaleem reacted angrily to the report, calling the Enough Project, a Washington-based anti-genocide group, "war mongers."

The Enough Project's report said there was a risk of a new civil war and warned that nationwide elections next year and a 2011 referendum on whether the oil-rich and semi-autonomous south should secede from the Khartoum-led north would not be free and fair.

The report placed the bulk of the blame on the ruling National Congress Party (NCP) of Sudanese President Omar Hassan al-Bashir, who was indicted in March by the International Criminal Court for suspected war crimes in Sudan's remote western region of Darfur. The report called for sanctions.

"Without a firm response from the international community, led by the United States, full-scale nationwide war is inevitable," said the report, written by Enough Project co-founder and former U.S. State Department and National Security Council official John Prendergast.

"This should involve a special outreach effort to China because of the vulnerability of its oil investments should war resume in the South," the report said. "The United States must, then, organize and lead a multilateral diplomatic surge in Sudan aimed at negotiating and consolidating national peace."

It recommended "multilateral asset freezes aimed at key members of the NCP who have enriched themselves as a result of the oil boom of the last decade in Sudan." The report also supported travel bans and denying Khartoum access to the debt relief it has been lobbying for.

Sudan's U.N. envoy Abdalhaleem rejected the report.