The U.N.'s top official is warning outside military action may be needed to stop what he calls ethnic cleansing in the strife-torn Darfur region in western Sudan.

U.N. Secretary-General Kofi Annan says he is very concerned about violence in Darfur and a growing number of reports of human rights violations.

"Last Friday, the United Nations Emergency Relief Coordinator reported to the Security Council that 'a sequence of deliberate actions has been observed that seem aimed at achieving a specific objective: the forcible and long-term displacement of the targeted communities, which may also be termed ethnic cleansing.' Mr. Chairman, such reports leave me with a deep sense of foreboding," the secretary-general said.

Mr. Annan warns the international community cannot stand idle in the face of the humanitarian crisis unfolding in Darfur.

Sudan's foreign minister, Mustafa Osman Ismail, says Sudan does not need military help in Darfur, but his government would welcome humanitarian aid.

The United Nations and private aid agencies call what is happening in Darfur the worst humanitarian catastrophe in the world today. Last year, war broke out between two rebel groups and the Sudanese government. Since then, the U.N. estimates thousands of people have been killed, up to 800,000 have been internally displaced and more than 100,000 Sudanese have sought refuge in neighboring Chad.

The rebel groups accuse the Khartoum government of arming Arab militias to loot and burn African villages. Independent observers, including Human Rights Watch, support the accusations, but the Sudanese government has denied them.

Mr. Annan says, at the invitation of the Sudanese government, a high-level team will investigate the nature of the crisis and see how access can be improved to those in need of assistance and protection.

"It is vital that international humanitarian workers and human rights experts be given full access without further delay," he said. "They need to get to the victims, They need to get to those who need help. If that is denied, the international community must be prepared to take swift and appropriate action."

But Mr. Annan says military action should be a measure of last resort.