By Elizabeth Blunt
BBC Africa analyst
The US Secretary of State is in western Sudan to see for himself an area where more than a million people have been forced from their homes.
The US has praised Sudan over its help with extremists
Colin Powell warned of action against Sudan if security in the Darfur province is not restored.
But why is the United States so interested in Sudan?
The relationship between Sudan and the United States is a curious one.
The Americans still list Sudan as a state sponsor of terrorism, and formal diplomatic ties are at very low level.
Yet by deploying a mixture of aid and sanctions, Washington has brought about major changes of policy in Khartoum.
The US government has been the godparent of the peace agreement that seems finally to have ended the war in the south of Sudan.
Cynics often claim American foreign policy is driven by oil.
Sudan does have oil, and African producers are an alternative to the increasingly turbulent Middle East.
But southern Sudan is never going to be a cheap or easy place to produce.
Other issues are more likely to be driving Washington's policy.
One is the pressure from right-wing Christian groups in the US, who have taken up the cause of their fellow Christians in Sudan.
Their lobbying - on the issues of slavery and the forcible imposition of Sharia law - helped get sanctions imposed on Sudan in 1997.
But the most urgent driving force is likely to be Sudan's place in President Bush's war against terrorism.
It has a radical Islamist government which hosted Osama Bin Laden in the early 90s; a number of attacks against US interests were planned from Sudan.
Since then the Americans have worked hard at persuading Khartoum to be more co-operative.
Osama Bin Laden was expelled, training camps were closed, and the US state department says Sudan has "deepened its cooperation in investigating and arresting extremists".
Colin Powell now has to tread a fine line between putting pressure on the Sudanese government over its activities in Darfur, and driving it back into the arms of America's enemies.