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The UK Foreign Secretary is urging British citizens in war-torn Sudan to make their way to the airfield "as soon as possible" as evacuation flights can no longer be guaranteed once the ceasefire expires.
James Cleverly said more than 530 people had been flown to safety on six flights as of 9pm on Wednesday.
Of those, 361 were UK citizens and the remaining 175 were of other nationalities, including dependents.
But Mr Cleverly said the UK "cannot guarantee" how many further flights will depart after the ceasefire ends on Thursday evening.
He urged UK citizens who wish to leave Sudan to make their way to the Wadi Saeedna air strip "as soon as possible".
On Sky News on Thursday morning, he said: "We cannot predict exactly when that ceasefire ends, but what we do know is that it will be much harder, potentially impossible [to run evacuation flights].
"So what we are saying to British nationals is if you're hesitant, if you're weighing up your options, our strong, strong advice is to go to Wadi Saeedna whilst the ceasefire is up and running.
"There are planes that have capacity. We will lift you out, and we are not able to make those same assurances once a ceasefire is ended."
Sudan crisis latest - in pictures
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A member of the Saudi Navy carries a child from a ship at Jeddah's port during the kingdom's evacuation of civilians from Sudan. Reuters -
Indian nationals evacuated from Sudan arrive at Indira Gandhi International Airport in New Delhi. EPA -
Sudanese refugees queue to receive aid from the World Food Programme near the border between Sudan and Chad in Adre, Chad. Reuters -
Tunisian citizens evacuated from Sudan leave a military aircraft upon their arrival at Tunis-Carthage International Airport. AFP -
Indians evacuated from Sudan arrive on a flight at the Indira Gandhi International Airport in New Delhi, India. AP Photo -
Moroccan nationals, who have been evacuated from Sudan, arrive at Mohammed V airport in Casablanca, Morocco. EPA -
A boat with 1,687 civilians from more than 50 countries fleeing violence in Sudan, arrives at King Faisal naval base in Jeddah, Saudi Arabia. AFP -
RSF fighters in the East Nile district of greater Khartoum. AFP -
Passengers disembark a plane from Djibouti at Roissy-Charles-de-Gaulle airport near Paris after being evacuated from Sudan. AFP -
Buildings destroyed in recent fighting in Khartoum, Sudan. AP -
Passengers fleeing the fighting in Sudan arrive at Wadi Karkar bus station in Aswan, Egypt. EPA -
Ali Mazloum, a Lebanese citizen who was evacuated from Sudan, is welcomed upon his arrival at Beirut airport. Reuters -
A woman helps another after fleeing clashes between the paramilitary Rapid Support Forces and the army in Khartoum. Reuters -
Soldiers attend to Greek citizens evacuated from Sudan as they disembark from a military aircraft in Attica, Greece. EPA -
People carry hibiscus juice and cold water for those being evacuated from Khartoum to Port Sudan. Reuters -
Thais wait to be evacuated by boat at a port in Sudan. EPA -
Greek citizens arrive from Sudan on a military plane in Elefsina, south of Athens. AFP -
Japan's senior Vice Foreign Minister Shunsuke Takei welcomes his country's citizens in Djibouti after they were rescued from Sudan. AFP -
A member of the Saudi Royal Navy carries a child who was rescued from Sudan, in Jeddah. Reuters -
A military plane carrying evacuees arrives at Ciampino Airport near Rome, Italy. Reuters -
Italy's Foreign Minister Antonio Tajani greets the country's ambassador to Sudan, Michele Tommasi, as he arrives at Ciampino Airport. Reuters -
South Korea's ambassador to Saudi Arabia, Park Joon-yong, at a Saudi Air Force base in Jeddah, where he met diplomats from his country evacuated from Sudan by the kingdom's air force. Reuters -
Having fled from Sudan, a South Korean nun disembarks from a military plane after landing at King Abdullah Air Base in Jeddah. AFP -
People gather as they seek to escape the violence in Khartoum. Reuters -
Spanish diplomatic personnel and citizens wait to disembark from a military plane after being evacuated from Sudan, in Djibouti. Reuters -
A closed pharmacy and shops in the south of Khartoum as battles rage in the capital between the army and paramilitaries. AFP -
Passengers from Sudan disembark from a Spanish Air Force plane at Torrejon Airbase in Madrid. AP -
People evacuated from Sudan arrive at a military airport in Amman. AFP -
Jordan was among those countries to have rapidly flown its citizens in Sudan to safety. AFP -
This child was one of those to have arrived safely in Amman. AFP -
A building in Khartoum burns as violence rages in Sudan. EPA -
Italian citizens are flown out of the Sudanese capital on a military aircraft. Reuters -
The fighting has caused heavy damage to parts of Khartoum. EPA -
Indonesian citizens travel on a bus during an evacuation operation in Khartoum. EPA -
A Spanish military aircraft takes off from Khartoum as European countries rescue citizens from Sudan. Reuters -
Jordanians arrive at a military airport in Amman after their evacuation from Sudan to escape the fighting. AP -
French troops arrive at an air base in Djibouti to prepare to evacuate about 100 people from Sudan. AFP -
Smoke rises from buildings during clashes between the paramilitary Rapid Support Forces and the Sudanese army in Khartoum. Reuters -
Saudis are met by Saudi Royal Navy staff as they arrive at Jeddah on the Red Sea after being evacuated from Sudan. Reuters -
The streets of southern Khartoum bear the scars of fighting between two factions of the Sudanese military. AFP -
A convoy leaves Khartoum for Port Sudan as fighting between military factions in the Sudanese capital continues. AFP -
A civilian convoy leaving Khartoum for Port Sudan. AFP -
Saudi citizens and people of other nations are evacuated by the Saudi Royal Navy from Port Sudan to escape the conflict. Reuters -
A photo from October 2017 of the US embassy in Khartoum. AFP -
Saudi citizens are met by Saudi Royal Navy staff as they arrive at Jeddah after being evacuated from Sudan. Reuters -
Smoke hangs over Khartoum as factions belonging to the Sudanese Army and the Rapid Support Forces go back to trading gunfire after a ceasefire failed. AP
Asked whether the UK may have to leave some of its citizens behind, Mr Cleverly said: "Well ... as a business it is really, really difficult to predict what might happen over the next couple of days.
"Now is the time to move because when this ceasefire ends, my ability to give the kind of limited assurance that I can give now might go and we might not be able to evacuate so please, please, please, get to the airfield today. You can come out. We have capacity, we have airframes."
Former British ambassador to Sudan, Dame Rosalind Marsden, told Sky News talks are ongoing to extend the halt in fighting.
“What we're looking at this morning is that this is an initiative by the local regional organisations to see if they can get the temporary truce extended by an another 72 hours that's been led by South Sudan," she said.
“The important thing there is to make sure that all the international actors and regional actors are co-ordinating together to be able to exert maximum pressure.”
Dame Marsden said the current ceasefire was "faltering". But moves were under way by the US to negotiate a permanent ceasefire.
“The current ceasefire is sort of faltering, but at least there's a lull in fighting, rather than advancing," she said.
"[There have] been calls in the UN Security Council yesterday, especially from the United States to set up a committee to try to negotiate a permanent ceasefire. But it's also important to make sure that the voices of civilian actors the pro-democracy, civilian leaders are also listened to."
Africa minister Andrew Mitchell said the evacuation mission was "going very smoothly" with "no great backlog, no great congestion" at the air strip.
But, he said, "we are absolutely in the hands of the ceasefire".
Mr Mitchell told Sky News: "We are doing everything we can to make sure it's prolonged and on the wider stage, too, trying to negotiate for a longer ceasefire, because if the combatants don't lay down their arms and return to barracks, there's going to be a humanitarian catastrophe in Sudan."
He said that "at the moment those safe and legal routes don't exist" for refugees from Sudan to claim asylum in the UK.
Only British passport holders and immediate family members with existing UK entry clearance are being told they are eligible to be flown out.
But Alicia Kearns, the Tory chair of the Foreign Affairs Select Committee, said elderly people dependent on children who are British citizens should also be admitted.
She told the BBC: "In the same way we treat children who are dependent on their parents, we should respect that some elderly people are dependent on their children.
"It is important that we are bringing people out who would otherwise be left destitute and really vulnerable."
