Only 9,000 troops of a planned 26,000-strong force have been deployed

Six members of the joint United Nations African Union peace mission in Sudan's Darfur region have been killed in an attack, a UN source has told the BBC.

Those who died included four Rwandan peacekeepers, one policeman from Ghana and another from Uganda.

State media reports that a convoy of 40 armoured vehicles ambushed the peace force while on patrol in North Darfur.

The UN-AU mission has been struggling to contain the violence and has just 9,000 of the planned 26,000 troops.

Reports say at least seven other peacekeepers were wounded and a number of others remain missing.

'Outraged'

Ten vehicles from the UN-AU Mission in Darfur (Unamid) were destroyed, Sudan's state media reports.

"The mission is obviously outraged by the attack," Unamid spokeswoman Shereen Zorba told Reuters news agency.

It is unclear who was responsible. Numerous armed groups operate in Darfur - rebel factions, pro-government militias and criminals.

Last week, Burkina Faso's Foreign Minister Djibril Bassole was appointed as the new UN and AU Darfur peace envoy.

Two outgoing peace envoys have questioned whether armed groups in the region are committed to ending the conflict.

Talks have been complicated recently because the rebels have split into more than a dozen factions.

Since the conflict began in Darfur five years ago, the UN estimates that some 300,000 people have died and two million have fled their homes.

The conflict began when rebels took up arms in protest at alleged government discrimination against the region.

Pro-government Arab militias have been accused of widespread atrocities against the black African population.