Since early 2003, the Darfur region in western Sudan has been wracked by violence that has forced more than 1.2 million to flee to refugee camps in the area and in neighboring Chad.
U.S. officials now say these refugees will begin dying in large numbers unless the violence ends and humanitarian aid begins flowing into the region.
"If nothing changes we will have 1 million casualties. If things improve we can get it down to about 300,000 deaths," Andrew Natsios, head of the U.S. Agency for International Aid, told Reuters en route to Sudan.
"Because a lot of the kids are already so malnourished, you just cannot bring them back," he said.
Officials with the World Food Program questioned the numbers given by Natsios, but agreed a huge population is in danger.
"What is clear is hundreds of thousands of lives are at risk. Unless we and the rest of the humanitarian community working in Darfur are properly resourced as soon as possible, we will have a humanitarian catastrophe on our hands," Marcus Prior, the program's spokesman in Khartoum, told Reuters.
Powell's trip, the highest-ranking visit to the African nation in more than two years, comes as aid efforts continue to face security obstacles. The secretary hopes to press the central government to improve access to the area and to stop its support for the Janjaweed, an Arab militia blamed for much of the violence.
Powell's arrival comes on the same day U.N. Secretary-General Kofi Annan warned the international body may also step into the conflict.
Asked about possible sanctions or other measures against the Khartoum government, Annan told reporters, "Depending on what we see on the ground, the council may have to take further steps."
The secretary-general is scheduled to visit Sudan this week and said his visit may prompt further action from the Security Council.
"The government has committed to disarm the militias and protect its people. This is one of the issues I will discuss with them," Annan said.
The United Nations has helped broker a cease-fire in Sudan's larger civil war, but Annan said any future assistance to maintain the peace there was dependent on the situation in Darfur.
"We cannot talk of comprehensive peace in Sudan if the gross and systematic abuse of human rights in west Sudan, Darfur, continues," Reuters quoted Annan as saying.
Annan and Powell plan to tour the Darfur region on Wednesday.
The crisis in Darfur erupted after the Khartoum government dispatched its troops and Arab militia to the region to quell a rebellion by African Muslims aimed at bolstering their role in the government.
The bloody reprisals have been aimed at both the rebels and anyone suspected of helping them. The Janjaweed militia has been accused of burning villages, killing men, women and children in retribution and sparking the mass exodus.