US President George W Bush has ordered a freeze on the assets of anyone felt to have posed a threat to stability in Sudan's strife-torn region of Darfur.
President Bush said continuing violence in Darfur posed an "unusual and extraordinary threat" to US policy.
Hollywood actor George Clooney, who visited Darfur, is urging Americans to take part in rallies across the US on Sunday to put pressure on Khartoum.
Violence in Darfur has killed more than 180,000 people and created 2m refugees.
Many of the attacks on civilians have been blamed on pro-government militias deployed to fight rebels.
The Sudan government denies backing the Janjaweed militia and blames Darfur's rebels for taking up arms three years ago.
'Heinous actions'
The presidential order also bars US citizens and companies from doing business with those whose assets have been frozen.
"These sanctions are aimed at those responsible for heinous actions being committed in Darfur," White House spokesman Scott McClellan said.
"The United States will continue to work with its international partners to provide humanitarian assistance, support human rights, and bring peace to Darfur."
The order by President Bush follows a UN Security Council resolution earlier this week placing sanctions on four individuals accused of war crimes in Darfur.
The four people named in the UN sanctions include two rebel leaders, a former Sudanese air force chief, and the leader of a pro-government militia.
It is not clear if they have any property in the US.
'21st-Century genocide'
The Hollywood actor, George Clooney, visited Darfur with his father, a journalist, last week.
The pair also visited neighbouring Chad where many Sudanese have fled.
Mr Clooney urged the public to attend rallies across the US on Sunday to pressure Khartoum to stop what Washington says is genocide against Darfur's black African population.
"What we cannot do is turn our heads and look away and hope that this will somehow disappear," Mr Clooney told a press conference on Thursday in Washington.
"It's the first genocide of the 21st Century," he said.
Hollywood actors, political and religious leaders and sporting personalities are expected to be among those attending the rallies.
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