President Bush has approved stiffer sanctions against Sudan to try to persuade it to stop the violence in Darfur.
Mr. Bush signed an executive order Friday that freezes the assets of those deemed complicit in the atrocities in Darfur and blocks their entry into the United States.
The president said in the order that Sudan continues to implement policies that violate human rights.
The action expands on earlier sanctions issued by President Clinton in 1997.
Meanwhile, the new U.S. envoy to Sudan, Andrew Natsios, has arrived in Khartoum to press the government there to accept U.N. peacekeepers in Darfur.
U.S. officials are pressing for the U.N. to replace an African Union peacekeeping force in Darfur. Critics say the AU force cannot adequately protect millions of civilians in Sudan's western region.
A U.S. Embassy official in Khartoum says Natsios hopes to visit both southern and western Sudan and meet with senior Sudanese leaders.
More than three years of fighting in the Darfur have killed an estimated 200,000 people and displaced more than two million others.
Some information for this report was provided by AP and Reuters.