World Bulletin / News Desk

 The United Nations on Monday said South Sudan has decided to expel the world body's top humanitarian official based in the conflict-torn nation and called on the government to immediately reverse its decision.

A U.N. statement said Secretary-General Ban Ki-moon condemned the move by the Juba government to expel Toby Lanzer of Britain, deputy head of the U.N. Mission in South Sudan as well as its humanitarian coordinator.

"The Secretary-General calls on the government of South Sudan to reverse its decision immediately," the U.N. press office said. "He further urges the government to cooperate fully with all United Nations entities present inSouth Sudan."

The statement said Lanzer has been "instrumental in addressing the increasing humanitarian needs of conflict-affected communities in the country, and ensuring that life-saving humanitarian assistance reaches the most vulnerable."

Lanzer's term was due to end shortly. The United Nations announced on Friday that his replacement will beEugene Owusu of Ghana.

South Sudan's U.N. mission did not respond immediately to a request for an explanation about Lanzer's expulsion. Lanzer is quite active on Twitter, where he often posts messages about the dire situation in the country to his nearly 12,000 followers.

Over 40 percent of South Sudan's 11 million people need food aid, according to figures from the Integrated Food Security Phase Classification.

Forces loyal to President Salva Kiir and rebels allied with former Vice President Riek Machar have been fighting for nearly 18 months in the world's newest state, which seceded from Sudan in 2011. Several ceasefires have been agreed but broken.

The U.N. Security Council has threatened to blacklist anyone undermining security or interfering with the peace process in South Sudan, but it has not yet imposed worldwide travel bans and asset freezes on any officials in the country.