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World powers were preparing for a possible evacuation from Sudan on Friday as fighting continues to rage.
The European Union is "working on different possibilities" to get people out of Khartoum, a senior official said.
Germany said more of its citizens were seeking help from their embassy in Sudan.
Britain’s Foreign Secretary James Cleverly has cut short a Pacific trip to focus on the crisis.
Western governments are scrambling to protect their citizens after aid workers were killed, an EU official was assaulted and UN offices were looted during the violence.
The UN's International Organisation for Migration announced on Friday that one of its staff had been killed in crossfire in Sudan.
"I am deeply saddened by the death of our humanitarian colleague, and join his wife and newborn child, and our team in Sudan in mourning," said the IOM's director general Antonio Vitorino.
UN officials raised their estimated toll to 400 dead and 3,500 injured amid clashes between Sudanese generals and paramilitary forces.
Japan on Friday sent a military transport plane to Djibouti that could rescue about 60 Japanese citizens from Sudan. South Korea said it would likewise station forces nearby.
The EU official said countries preparing possible rescues from Khartoum "will be following closely the situation to wait for the moment that it can be done".
"For the time being, the assessment of those on the ground, including the EU embassy, is that the security conditions are not in place for going ahead with an operation of this kind," they said.
German Foreign Minister Annalena Baerbock chaired an emergency task force on Friday as military planners ponder their options.
Embassy staff are finding it harder to contact people as electricity supplies fail and phone batteries run out, a spokesman for the foreign ministry said in Berlin.
He said a number of people in the "low three digits" had registered with the embassy to receive updates on a possible evacuation.
The figure has risen in recent days from an earlier estimate of 150, the spokesman said.
"The situation on the ground remains drastic," he said.
Berlin is reportedly preparing a rapid-response force and could turn to the few dozen Bundeswehr troops already deployed to a UN mission in South Sudan.
It did not deny reports that a transport plane had been stationed in Jordan.
Charity bosses said people fleeing Khartoum may need assistance in Chad and South Sudan, as rescue planners face the difficult task of grouping evacuees in the capital.
Countries including Britain and Germany have said they are considering all options for a possible rescue mission. Western powers are drawing up lists of their citizens in Sudan.
More than 300 people have died since fighting broke out in the African nation between army generals and the paramilitary Rapid Support Forces.
Dutch marines and medical teams have been deployed to Jordan even as the Netherlands said an evacuation from Sudan was not currently possible.
France urged its citizens in Sudan to remain in their homes as it tries to broker a humanitarian ceasefire.
Outside Europe, the Pentagon said it was “deploying additional capabilities” in the region to prepare a possible rescue of US embassy staff.
However, the closure of an international airport in Khartoum means “it’s not safe to undertake a US government co-ordinated evacuation of private American citizens at this time,” State Department spokesman Vedant Patel said on Thursday.
Nato countries rescued thousands of people from Afghanistan after the Taliban seized power in 2021, but were criticised for a lack of planning.
EU members agreed to establish a 5,000-troop rapid response force to better co-ordinate missions but it has yet to take shape.
One of Mr Cleverly’s predecessors, Dominic Raab, was heavily criticised for staying on holiday while the Taliban conquered Afghanistan two years ago. He was demoted a month later.
“It’s with real regret that due to the ongoing situation in Sudan I’ve had to cut the visit short,” said Mr Cleverly after he cancelled stops in Samoa and New Zealand.
The British High Commission in Wellington said Mr Cleverly had made a series of calls from its offices.
He said on Friday he had spoken to French Foreign Minister Catherine Colonna about their “mutual concern for French and British citizens in Sudan”.
“Alongside our international partners, we call for a lasting ceasefire,” he said.
Mr Cleverly was in the Pacific after a meeting of G7 foreign ministers in Japan, where they discussed the crisis in Sudan.
They called on both sides to “renounce violence, return to negotiations, and take active steps to reduce tensions”.
Gunfire was reported on Friday despite appeals by world powers for a ceasefire marking Eid Al Fitr, the end of Ramadan.
Britain said it was unclear which side was responsible for starting the violence, which has undermined hopes of a transition to civilian rule after a coup in 2021.
