"I hope to give them a very direct message about how the United States and the international community see the horrific situation," Powell told reporters on Tuesday on his plane from Turkey.
"We need to see action promptly," he added. A senior US official said earlier on Tuesday that up to one million displaced Sudanese could die this year in Darfur region because of a humanitarian crisis blamed on Khartoum.
One million Darfuris have fled their homes in the past 18 months because of the conflict in the arid region between the militias known as the Janjaweed, the government and two rebel groups who say they are acting to protect the villagers.
UN officials and human rights groups have said the Janajweed are carrying out ethnic cleansing. Some organisations have likened it to the genocide in Rwanda in the 1990s.
Relief organisations are racing to take food and medicine to camps for displaced people before the imminent rainy season cuts off vast part of the region.
"We see indicators and elements that would start to move you toward a genocidal conclusion but we're not there yet"
US Secretary of State
Powell said he would tell the Sudanese government to bring the Janajweed under control and end restrictions on aid to the roughly two million people affected by the conflict.
"People are dying and the death rate is going to go up significantly... We see indicators and elements that would start to move you toward a genocidal conclusion but we're not there yet," the secretary of state said.
The Sudanese government rejects allegations that it supports the Janjaweed and says it has launched a campaign to disarm both them and the rebel groups.
Promise of access
In a speech in Khartoum shortly before Powell arrived, Sudanese President Umar Hasan al-Bashir said his government would redouble its efforts to secure access to the needy.
Analysts say the Sudanese army has worked with the Janjaweed but the militia is not completely under its control. The government has limited resources to impose law and order in an undeveloped region the size of France.
One million Darfuris have fled
their homes in the past 18 months
Making the first visit to Sudan by such a senior US official in more than two decades, Powell declined to specify what threats he would make when he meets Sudanese leaders later on Tuesday if they reject his demands.
But he warned that the United States is working on a UN resolution about Darfur which could lead to international sanctions against Africa's largest country.
Sudan could also miss the benefits, such as improving relations with Washington, which it expects for resolving a separate conflict in the south earlier this year, he added.
Criticised for responding too slowly to the crisis and under pressure in Congress to do more, Powell will meet UN Secretary-General Kofi Annan in Khartoum on Wednesday and visit Darfur to see the catastrophe for himself.
Andrew Natsios, head of the US Agency for International Development, said earlier there was little the international community could now do to stop about 300,000 people dying in the region this year and the toll could be up to one million people.
The spokesman for the UN World Food Programme in Khartoum, Marcus Prior, said it was premature to make such predictions.