South Sudan conflict: UN condemns expulsion of Toby Lanzer
The United Nations has condemned the expulsion of the UN humanitarian co-ordinator in South Sudan, Toby Lanzer.
Mr Lanzer, a UK citizen, was given no explanation as to why he had been asked to leave the country, the UN said.
UN Secretary-General Ban Ki-moon called on the government to reverse the decision immediately.
Months of fighting have left an estimated 40% of South Sudan's population in need of food aid and more than two million have been displaced.
A spokesman for Mr Ban said Mr Lanzer had been "instrumental in addressing the increasing humanitarian needs" of the people.
"The secretary-general calls on the government of South Sudan to reverse its decision immediately. He further urges the government to co-operate fully with all United Nations entities present in South Sudan," a statement said.
The UN said Mr Lanzer was not in South Sudan on Monday but he planned to return to wrap up final business.
Mr Lanzer was coming to the end of his term and the UN had already announced he was to be replaced by Eugene Owusu of Ghana.
South Sudan is the world's newest state, having gained independence from Sudan in 2011.
But violence broke out in December 2013 when President Salva Kiir accused his sacked deputy, Riek Machar, of plotting a coup.
Mr Machar denied the allegation but then formed a rebel army.
Government forces have recently been advancing towards Leer, Mr Machar's birthplace.
BBC Southern Africa correspondent Karen Allen says the UN has stopped short of imposing sanctions on South Sudan's politicians but there is now a renewed sense of urgency to step up efforts to hold the leadership to account.
Earlier this month, Mr Lanzer warned that more than 300,000 people were without access to vital aid because of fighting in Unity state.
"Ongoing hostilities in Unity state have now obliged all non-governmental organisations and UN agencies to evacuate staff from Leer and other locations," he said.