"Clearly, Darfur needs help from the rest of the world"
Jack, Houston, USA
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Casey told reporters: "We are consulting with the British now about what we might be able to do in terms of an additional Security Council resolution on Sudan."
"We need to look at what kinds of measures we can take to try and encourage a change of heart by the Sudanese government," he said.
New sanctions could also include restrictions on companies that do business in Sudan denominated in US dollars, although the US has not said when it might impose these measures.
Emyr Jones Parry, Britain's UN ambassador, had already spoken on Tuesday in favor of a UN resolution on sanctions on Sudan but with China a major consumer of Sudanese oil, such a measure could run into opposition from other Security Council members.
"The international community has shown great patience with Sudan ... Our patience has largely run out, particularly in light of these new delaying tactics"
State Department deputy spokesman
More than 78,500 Darfurians fled their homes in January and February, while a UN report estimates about 2.2m people have been displaced by the violence in the region of western Sudan.
More than 200,000 people have been killed over the course of the conflict as armed groups have been fighting with government forces and Janjawid fighters for more than three years.
Khartoum is accused of supporting the Janjawid, a pro-government, Arab militia, that has committed many of the worst atrocities in the conflict.
The UN has been attempting to get Khartoum to agree to a hybrid force of UN and African Union troops to try to stem the violence in Darfur.
Sudan rejects UN requests
But Omar al-Beshir, the Sudanese president who has already rejected a number of US requests that it permit international intervention in Darfur, sent a letter to the UN last week backtracking on an agreement to permit up to 20,000 peacekeepers, armed and led by the UN, into Darfur.
"The international community has shown great patience with Sudan," said Casey. "Our patience has largely run out, particularly in light of these new delaying tactics."
Washington has described the situation in Darfur as "genocide".
Andrew Natsios, the US envoy to Sudan, said it was up to George Bush, the US president, to announce proposed US sanctions on Sudan.
"Enough is enough," he said. "It's pretty clear the [US] president is angrier than anyone else on this. He gets very upset when he talks about this situation."
Natsios said measures against Sudan were discussed in a number of government meetings before he left for Sudan earlier this month.
But he did not provide the names of companies operating in Sudan that might be affected by new sanctions.
Save Darfur, a coalition of human rights groups, launched a campaign of television and newspaper advertisements this week calling on Bush to implement the long-threatened US "plan B".
"Secretary Rice, president Bush, diplomacy alone has failed. You said it was time to act. So act now!" says the ad.