Washington ? Thousands of people joined celebrities and lawmakers at a rally Sunday urging the Bush administration and Congress to help end genocide in Sudan’s Darfur region.

“Not on our watch!” the crowd chanted as a parade of speakers lined up for their turn on a stage on the National Mall, the Capitol serving as a backdrop.

“The personal motivation for a lot of us is the Holocaust,” said Boston-based Rabbi Or Rose of Jewish Seminarians for Justice. “Given our history and experience, we feel an obligation to stand up and speak out.”

In an interview, refugee Hassan Cober said he was forced to leave his family and flee Sudan four years ago after many were killed and raped. He urged the United States and the United Nations to act quickly, saying he had no idea where his family was or if they were OK.

“We need deeds, not words,” said Cober, now of Portland, Maine. “They need to come to Darfur today, not tomorrow, because what is going on is a disaster.”

The organizers’ permit anticipated 10,000 to 15,000 people would rally, one of several in U.S. cities this weekend against what the United Nations calls the world’s worst humanitarian disaster.

Thousands of people gather on the National Mall in Washington to protest the genocide in the Darfur region of Sudan. Actors, athletes and activists concerned about the atrocities in Darfur region joined politicians and religious leaders in urging a greater U.S. role in ending what the United Nations says is the world's worst humanitarian disaster.

“It is the socially responsible, good conscience thing to do,” said Ron Fisher, who took a pre-dawn bus from Cleveland with his 15-year-old daughter, Jordyn. “It’s an opportunity to show my daughter what people do when they care about something.”

The U.S. Park Police, which does not issue crowd estimates, reported no arrests.

The event attracted high-profile speakers such as actor George Clooney, just back from Africa; Sen. Barack Obama, D-Ill.; House Democratic leader Nancy Pelosi, of California; Nobel Peace Prize winner Elie Wiesel; Olympic speedskating champion Joey Cheek, who gave his bonus money to the cause; and Roman Catholic Cardinal Theodore McCarrick, archbishop of Washington.

“If we care, the world will care,” Obama said. “If we act, then the world will follow.” Pelosi said Democrats for once agree with Bush: “This genocide must stop.”

Clooney and his father, Nick, a former television anchorman, interviewed families in Sudanese refugee camps. The elder Clooney described their role as reporters. “It’s our job to tell you what we saw,” he said. “Thousands of people hanging on by the most gossamer of threads.”

His son was the event’s big draw. He said the United States’ and United Nations’ policies are failing – and citizens must demand change. “This is in fact the first genocide of the 21st century, but there is hope: all of you,” the actor said. “Every one of you speaking with one voice, every one of you.”