His spokesperson says Mr Guterres has called on all warring parties to stop fighting and commit to a durable cessation of hostilities.

“He is highly worried about the increasing ethnic dimension of the violence, as well as by reports of sexual violence,” Stéphane Dujarric said.

“With nearly nine million people now urgently requiring humanitarian aid and protection in Darfur, he stresses the need for an end to looting and widened access so aid can reach those who most need it.”

Earlier the UN's head of mission for Sudan, Volker Perthes, said these attacks appeared to have been committed by Arab militia and the paramilitary Rapid Support Forces (RSF).

“These reports are deeply worrying and, if verified, could amount to crimes against humanity,” he said in a statement.

Meanwhile, Saudi Arabia has announced it will jointly lead a conference on the humanitarian response to the war in Sudan next week. Saudi Arabia and the US have been trying to mediate in the eight-week conflict between the army and the RSF.