The United States plans to announce tough new sanctions against Sudan today before working out a resolution in the United Nations in an intensified effort to end the bloodshed in Darfur.
President George W Bush will announced punitive action against 31 companies and four individuals, according to a draft of a speech he will make later today.
"President Bashir's actions over the past few weeks follow a long pattern of promising co-operation while finding new methods of obstruction," Bush will say.
The ratcheting up of US pressure coincides with a broader effort by United Nations officials to get Sudan's government to end the violence that has devastated Darfur since 2003.
Fighting by government-backed militias and rebel groups in the Darfur region has killed more than 200,000 people and driven about 2 million from their homes.
In 2004, the UN Security Council adopted a resolution calling on Sudan to end the attacks.
But Mr Bush and other top US officials have grown increasingly impatient with Sudan President's Omar Hassan al-Bashir's reluctance to stop attacks by Arab militias, widely believed to be supported by the government.
Mr Bashir also stalled for months in accepting UN peacekeeping support packages to the African Union of 7,000, a prelude to a larger force of more than 23,000 troops and police.
He received plans for that force only last week but has said the number of military personnel was far too large.
New US sanctions against Sudan would extend those implemented in 1997 and be aimed mainly at companies owned or controlled by the Sudanese government.
The companies targeted include firms in the oil and petroleum export-related businesses, crucial to Sudan's economy.
The four individuals affected include senior Sudanese government officials and rebel leaders.
"This will be the first time we are taking such an action ahead of the United Nations," said a senior administration official.
The UN Security Council last year imposed sanctions on four mid-level individuals.
The US and Britain are also considering drafting a UN resolution that would impose an arms embargo on all of Sudan, not just Darfur.
It would increase the number of people subject to sanctions and monitor airports in Sudan to determine who is breaking previous resolutions on offensive military flights.
China, a major customer for Sudan's oil and a permanent Security Council member, said it opposed expanded sanctions.
"Expanding sanctions can only make the problem more difficult to resolve," China's representative on African affairs, Liu Guijin, told a news conference in Beijing.
Asked whether China would veto any new UN resolution targeting Sudan, he said: "It's still too early to speak of."
Last month Mr Bush vowed to hold off imposing new sanctions against Sudan to give the United Nations more time to negotiate with Khartoum over accepting a peacekeeping force in Darfur.
"The President believes we cannot wait any longer for the violence to stop and the people of Sudan to be given what they need," the US official said.