US Secretary of State Condoleezza Rice has arrived in Senegal at the start of a trip that will take her to Sudan and the Middle East.
She will attend an African economic conference before heading to Khartoum.
However, her visit to Africa has been cut short so that she can visit Israel and the West Bank later this week.
The Middle East trip is a sign of US concern about an upsurge in violence, says BBC correspondent Jonathan Beale.
Ms Rice is visiting Africa for the first time since taking over as secretary of state earlier this year.
During her trip to Senegal, she is expected to highlight US efforts to improve trade ties with developing countries promoting democratic reform.
In Sudan, she will press for improved security and aid relief in the western Darfur region, where she will visit a refugee camp.
"I'll try to say to people that there is hope, that nobody is forgotten, that we are working very very hard," Ms Rice said ahead of her visit.
"I'll talk to the non-governmental organisations that are on the front lines.
"And I'll say that even the darkest moments in any country can be overcome. It's a very horrible situation."
Our correspondent, who is accompanying Ms Rice, says President George W Bush has come under pressure back home to do more on Darfur.
More than two million people have been displaced and some 180,000 have died during two years of conflict in Darfur between rebels and government forces.
Later this week, Ms Rice will head to Israel and the Palestinian territories - her third trip to the region in five months.
The US state department says Ms Rice will be urging both Palestinians and Israelis to do more to ensure that next month's Israeli pull-out from Gaza and parts of the West Bank goes ahead as planned.