United Nations ? Actor George Clooney on Thursday warned the U.N.’s most powerful body Thursday that if it did not send peacekeepers to Sudan’s Darfur region, millions would die in the first genocide of the 21st century.

Clooney and his journalist father, Nick Clooney, spent five days in Darfur in April, gathering personal stories of the death and suffering that have ravaged the African region. Both have worked since their return to publicize the plight of the people there.

The mandate of African Union peacekeepers in Darfur expires at the end of the month and the Sudanese government has rejected their replacement by a U.N. force. If U.N. forces are not sent to replace them, George Clooney warned the U.N. Security Council that all aid workers would leave and the 2.5 million refugees who depend on them would die.

More than 200,000 people have been killed in the Darfur conflict and more than 2 million have fled their homes since 2003 when ethnic African tribes revolted against the Arab-led Khartoum government.