"As we speak we are under attack by government troops in about 40 cars and about 600 Janjaweed (militia)," Khalil Abdallah, the political secretary of the rebel National Movement for Reform and Development (NMRD), told Reuters from Darfur.

"This shows they are not respecting the ceasefire agreement at all," Abdallah said.

The rebel splinter group, based mainly along the border between Sudan and Chad, was formed early last year after commanders split from the leadership of one of the two main Darfur rebel groups.

Janjaweed is the name given by Darfur rebels to Arab militia which rebels, human rights groups and the United Nations say the Sudanese government has used to help put down the uprising, which began in early 2003.

The NMRD and the Sudanese government signed a ceasefire in December but talks mediated by Chad have since broken down.

The NMRD has accused the Janjaweed of attacks since the truce was signed and has refused to continue peace talks until Khartoum gives compensation for the attacks.

Abdallah said Monday's attack was about 25 kilometres (16 miles) east of their headquarters in Jabel Moun in West Darfur in an area where the rebels have two camps.

The Sudanese armed forces spokesman's office said they were not authorised to comment.

The two main Darfur rebel groups are stalling a return to separate peace talks with Khartoum in Nigeria, saying they want recommendations of a U.N.-appointed commission implemented so that 51 people can be tried for alleged war crimes in Darfur before talks can reconvene.

The U.N. Security Council is divided on the issue.