Unidentified assailants have killed three Rwandan peacekeepers in Sudan's Darfur region.
Monday's attack is the latest assault on members of Unamid, a joint peacekeeping mission by the UN and the African Union.
More than 20 camouflaged attackers opened fire on the soldiers as they guarded civilian engineers building a Unamid base in the mountainous Jabel Mara area, the peacekeeping force said in a statement.
A Unamid official said on condition of anonymity that three attackers were also killed in the hour-long gun battle that ensued.
Ban Ki-moon, the UN secretary-general, has called on Khartoum to arrest the attackers.
Surge in fighting
Aid workers say they have been unable to get access to large parts of eastern Jabel Mara since February, when there was a surge in fighting between Sudanese army forces and rebels.
The Unamid force, made up of mostly African soldiers and police, took over from a African Union mission. It is still short of its expected strength of 26,000 and is supposed to keep the peace in an area the size of Spain.
A total of 27 Unamid police officers and soldiers have been killed in attacks since the force came to Darfur in 2008, Unamid said.
A Unamid patrol travelling towards Jabel Mara in March was ambushed and held overnight. Five Rwandan peacekeepers were killed in two attacks in Darfur in December.
Violence flared in the mostly desert region in 2003 when rebels demanding more autonomy for the territory launched a revolt against Sudan's government.
Sudanese government troops and allied fighters launched a counter-insurgency campaign which Washington and some activists called genocide.
Khartoum dismisses the accusation and accuses the Western media of exaggerating the conflict.