The UNAMID soldiers and police were ambushed on a routine patrol by about 40 vehicles full of armed militia in North Darfur on Tuesday, UNAMID spokeswoman in Sudan Shereen Zorba told Reuters.

It was not immediately clear if the militias were government allies.

At the United Nations in New York, spokeswoman Michele Montas said the attack lasted two hours and the assailants used heavy weapons. UNAMID forces returned fire, Zorba said.

It was the worst direct attack on UNAMID forces since they began work on December 31.

"The secretary-general condemns in the strongest possible terms this unacceptable act of extreme violence against AU-U.N. peacekeepers in Darfur," Montas said, urging the Sudanese government to bring the perpetrators to justice.

Darfur's main rebel groups, including the Justice and Equality Movement (JEM) and the Sudan Liberation Movement Unity faction, denied any involvement.

"We, as JEM, from our side strongly condemn this kind of behaviour from any group which is against international law," said JEM deputy chief of staff Suleiman Sandal.

"We cooperate with the hybrid force at all times."

Sudan's army said it had no relation to the attack.

HOSTILE

France, which holds the rotating EU presidency, condemned the attack and called on all sides to cooperate to establish who was responsible.

There was confusion over the number of dead for several hours. Sudan's state news agency SUNA had earlier reported that five peacekeepers were killed in an attack in the western Sudanese region and 17 were missing.

Zorba said: "The final confirmation is seven killed, 22 injured. No one is missing. Everyone has been accounted for."

Arab militias mobilised by Khartoum to quell a revolt by non-Arab rebels in 2003 have been hostile to the U.N. troops in the past fearing they could arrest anyone indicted by the International Criminal Court for war crimes.

While some have since become disillusioned with the government and had turned against it, most have retained their weapons and many have been incorporated into official Sudanese military units.

At full strength, the UNAMID mission would be the world's largest U.N.-funded peacekeeping operation with 26,000 soldiers and police, but it has less than 10,000 personnel on the ground.

UNAMID commanders have urged the international community to provide troops quickly to reinforce the mission. They have also asked industrialised nations to provide vital equipment such as attack helicopters to help restore law and order in Darfur.

The conflict sparked the world's largest humanitarian operation, helping more than 4 million people affected by the fighting. International experts estimate some 200,000 people have died in Darfur.

UNAMID took over from a struggling African Union peacekeeping force which had been targeted by Darfur's warring parties, many of whom said the AU was not neutral.