UN chief Ban Ki-moon has condemned an ambush which left seven members of the joint UN-African Union peace mission to Sudan's Darfur region dead.
The Janjaweed has long been hostile to UN troops in Sudan, fearing they could be used to arrest anyone indicted by the court at the Hague, our correspondent says.
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.