Foreign Secretary James Cleverly has urged all UK nationals wishing to flee Sudan to come forward “as quickly as possible” despite a three-day extension to the ceasefire being agreed.
The British evacuation mission was potentially bought more time when the rival generals made the deal as the midnight deadline for the resumption of fierce fighting loomed.
The RAF has airlifted nearly 900 people from an airfield near the capital Khartoum but thousands more British nationals may remain in Sudan.
Flights were scheduled to continue regardless but intensified clashes would add extra pressure to the operation and Mr Cleverly had warned that the mission could become “impossible”.
However, the paramilitary Rapid Support Forces joined the Sudanese military in agreeing to extend the 72-hour truce that has seen fighting lull to allow citizens and foreign nationals to flee.
Mr Cleverly said: “The UK calls for its full implementation by the generals.
“I urge all British nationals wishing to leave to proceed to the airport as quickly as possible to ensure their safety.”
Britain had been urging the rival generals to extend the ceasefire, which should help stave off a feared humanitarian crisis in Africa’s third largest country.
More than 2,000 British nationals in Sudan have registered under the evacuation plans but the true number of citizens there could be far higher.
As of 4pm on Thursday, the Foreign Office said that 897 people had been evacuated over eight RAF airlifts.
The flights were however scheduled to run past midnight and around 1,000 people are expected to have been lifted to safety by Friday morning.
Military chiefs say they have the capacity to fly at least 500 people per day out of the Wadi Saeedna airfield, north of Khartoum.
Earlier in the day, Mr Cleverly warned that resumption of fighting could jeopardise the evacuation efforts.
“We cannot predict exactly what will happen when that ceasefire ends, but what we do know is it will be much, much harder, potentially impossible,” he told Sky News.
“So, what we’re saying to British nationals is if you’re hesitant, if you’re weighing up your options, our strong, strong advice is to go through Wadi Saeedna whilst the ceasefire is up and running.
“There are planes, there is capacity, we will lift you out. I’m not able to make those same assurances once a ceasefire has ended.”
Downing Street rejected calls from people, including Foreign Affairs Committee chairwoman Alicia Keans, to widen the eligibility for evacuation beyond British passport holders and their immediate family.
But the Prime Minister’s official spokesman said: “There is an element of discretion for people on the ground as you might expect, given the circumstances and the challenging situation people will be facing.
“We recognise these are very challenging circumstances and, as we have done on previous occasions, we obviously empower people on the ground to make decisions.”
The diplomat, who was not in Sudan when the fighting broke out, was being relocated from London to Addis Ababa in Ethiopia to play a key role in efforts to end the fighting.
Africa minister Andrew Mitchell warned that an end to the ceasefire could result in a humanitarian catastrophe in Sudan.
“It is essential that a ceasefire is maintained and that a political process is secured,” he told the foreign affairs think tank Chatham House.
“If not, the humanitarian consequences will be incalculable.”