Officials said the Bush administration as well as Western governments have concluded that the Khartoum regime plans a major sping operation in Darfour that could begin in May. They said the military operation was meant to precede plans by the United Nations and African Union to deploy 3,000 peace-keepers to Darfour by July 2007. Sudan has agreed to the peace-keeping force, meant to be supported by six attack helicopters.

"The situation remains very precarious and very unpredictable," Deputy Secretary of State John Negroponte said during a visit to Khartoum on April 16. "And I would say it continues to be fraught with danger."

"I'm also looking at what steps the international community could take to deny Sudan's government the ability to fly its military aircraft over Darfour," Bush said Wednesday. "And if we don't begin to see signs of good-faith commitments, we will hear calls for even sterner measures. The situation doesn't have to come to that."

A report prepared for the Security Council asserted that Khartoum has been transporting heavy weapons into Darfour, where more than 200,000 people have been killed in a rebel war since 2004. The UN study, first reported by the New York Times, said the Sudanese Air Force has airlifted heavy weapons aboard aircraft painted white to disguise them as UN or AU aircraft.

The report said the air force has been conducting air attacks and surveillance missions on suspected rebel areas of Darfour. At the same time, Sudanese ground forces were attacking villages in nighttime operations.

"Sudan's government has moved arms to Darfour, conducted bombing raids on villages," Bush said. "They've used military vehicles and aircraft that are painted white, which makes them look like those deployed by humanitarian agencies and peacekeeping forces."