John Danforth, the new US ambassador to the United Nations, said the UN Security Council members would begin negotiations on Thursday on a US-drafted resolution that imposes an arms and travel ban on militia leaders accused of atrocities in Darfur.
"We are talking about days. We are talking about this week. This is a matter of urgency," Danforth said on Wednesday.
The resolution, which threatens to escalate the sanctions within 30 days if results are not evident, could be expanded to include some bans against Khartoum, the diplomat said.
"Thirty days is too long for the government to act," Danforth said. "Sudan is clearly on a short leash."
"We are talking about days. We are talking about this week. This is
a matter of urgency"
US ambassador to UN
The United Nations describes the situation in Darfur in western Sudan as a terrible humanitarian disaster. After African groups rose up in revolt last year, Khartoum is accused of having unleashed militias to brutalise civilians in the arid region.
Some 10,000 to 30,000 people are estimated to have died in the conflict. A million were forced out of their villages and two million people are in desperate need of aid.
Germany, France, UK and Romania have strongly supported the US resolution.
UN Secretary-General Kofi Annan has said he believes the Sudan Government used planes, helicopter gunships and ground troops against the population.
The Janjawid militia then followed with "horrendous clean-up attacks" replete with "killing, plundering, burning and widespread rape", he said.