Sudan should accept an international peacekeeping force in Darfur or face tough sanctions, a group of 15 former foreign ministers has said.
About 2.5 million people in Darfur have been made homeless
The group, including former US top diplomat Madeleine Albright, said they want Sudan to accept a joint UN-African Union force by the end of this year.
Sudan has so far refused to allow UN peacekeepers to augment the AU force.
Three years of fighting have left at least 200,000 people dead and made another 2.5 million homeless.
"As former diplomats, we support one last effort to persuade Khartoum to accept the proposal for a hybrid force," the group wrote in the Financial Times newspaper.
If President Omar al-Bashir continues to refuse a joint force, sanctions should be applied, say the former diplomats, who come from Thailand and Turkey as well as Europe and the US.
These would include travel bans on military and civilian leaders, the freezing of assets, and measures to target Sudan's oil revenue and limit sales of equipment needed to produce oil, the group said.
But it does not call for is any kind of military action - including a naval blockade of Port Sudan, which would cut Sudan's oil exports at a stroke.
Nor does it include the idea of enforcing a flight ban over Darfur, which has been under consideration at the UN.
The UN has proposed that the current weak AU force of 7,000 soldiers be bolstered with more money and equipment supplied by the UN, eventually merging with UN troops into a hybrid force.
The violence has escalated sharply in Darfur in the last several weeks.
Late last week, the AU blamed the deteriorating security situation on the re-emergence of the pro-government Arab Janjaweed militias, and urged Khartoum to disarm the groups.
Aid agencies have withdrawn 250 workers this month, leaving many in Darfur vulnerable.
There are also fears that the fighting is destabilising neighbouring Chad where there has been an upsurge in violence.
The conflict began in early 2003, when a rebellion by local groups triggered a counter-offensive by the army and government-backed Arab militias.
Sanctions have been proposed before, but so far they have made little progress.