Mr Bush met with Mr Minnawi in the White House

Mr Minnawi, who visited the White House, heads the Sudanese Liberation Army (SLA), the only rebel group to sign a peace deal with the government.

Mr Bush also told Mr Minnawi the SLA had to stop instigating violence.

He asked Mr Minnawi to form alliances with two other Darfuri factions yet to sign the deal at a White House meeting.

Some 2m people have fled their homes in the Darfur region, and violence has continued. Tens of thousands of people are reported to have been killed in the ongoing violence.

Who are Darfur's rebels?

Two other Darfur rebel groups refused to sign up to the peace deal saying the terms were inadequate.

The Sudanese government remains strongly opposed to the idea of a UN force replacing the current African Union force, which is seen as too small and too poorly-funded to be effective.

Renewed violence

Mr Minnawi has said he has no opposition to the use of UN troops in the region.

Darfur has been in the grip of violence since the rebellion was launched three-and-a-half years ago.

While the peace agreement has had an effect in some areas, the UN says that fighting between the rival rebel factions is bringing renewed violence.

Mr Minnawi is to become senior assistant to the military president, Omar el-Bashir, which would also make him head of what will be the Darfur Authority.