"From Addis Ababa, he will lead the UK's diplomatic efforts in the region to bring fighting to an end in Sudan," the British Foreign Office said in a statement.

So far, six flights had evacuated 536 British nationals from Sudan, the UK authorities said. But there has been criticism of the slowness of the UK government's evacuations compared with other Western countries.

Sudan’s army and the Rapid Support Forces (RSF) paramilitary group have agreed to extend the truce that was coming to an end for another 72 hours.

The ceasefire and its extension had been brokered by the United States and Saudi Arabia.

The existing truce, which was to expire at midnight Thursday, has not stopped the fighting between the two sides but created some lull for tens of thousands of Sudanese to flee to safer areas and for foreign nations to evacuate hundreds of their citizens.