Omar al-Bashir, Sudan's president, has objected to UN plans to include soldiers from Nepal, Thailand and Scandinavian countries in the peacekeeping force for Darfur.

Onus on Sudan

The Scandanavian ministers said: "Sudan must bear the full responsibility for the situation that has now arisen.

"Norway and Sweden are being prevented from contributing to this very necessary effort, which was aimed at improving security for the  people of violence-ridden Darfur."

Unamid took over from the AU on January 1.

Currently, most of the force comes from the 7,000 existing AU soldiers who have been trying to bring peace to Darfur for the past three years. 

The Darfur mission, the UN's largest, will eventually consist of 20,000 troops and 6,000 police and civilian personnel, but only around 9,000 troops and police are currently in place.

US condemnation

In another development, the US on Wednesday pressed for tougher sanctions against Khartom after denouncing what it said was a blatant attack by Sudanese forces on UN peacekeepers in Darfur.

Sean McCormack, a state department spokesman, said: "The United States condemns the January 7 attack by the Sudanese Armed Forces on United Nations peacekeepers who were travelling in a supply convoy in Darfur.

"The United States believes this incident demonstrates the need  for a stronger arms embargo for Sudan and we will be working with our Security Council partners to that end."

The convoy was taking food and fuel to a Unamid base near the town of Tine, close to the border of western Darfur and Chad.

Crisis genesis

The Darfur conflict began in February 2003 when ethnic African tribes rebelled against what they consider decades of neglect and  discrimination by the Arab-dominated Islamist government in Khartoum.

The government's response was to back the Janjawid militia and give it free rein to crackdown on the anti-government fighters and their suspected civilian supporters.

At least 200,000 people have died and more than two million have fled their homes since the conflict began.