A New Zealand lawmaker who has led UN aid efforts worldwide is to be named UN mission chief in South Sudan, one of the worlds toughest peacekeeping jobs, diplomats said Wednesday.

UN Secretary-General Ban Ki-moon has sent a letter informing the Security Council of his intention to appoint David Shearer as the UN envoy to South Sudan and head of UNMISS, succeeding Ellen Margrethe Loj of Denmark.

Shearer, a 59-year-old member of New Zealand's parliament, served as UN deputy envoy in Iraq from 2007 to 2009, following UN assignments in Afghanistan, Lebanon, Israel, Rwanda, Liberia and the Balkans.

The United Nations has some 14,000 peacekeepers in South Sudan, where a civil war has been raging since December 2013.

The peacekeepers have come under heavy criticism for failing to protect civilians, including women who were raped by government soldiers in Jubly, not far from the gates of a UN compound in Juba.

Ban last month warned the council that South Sudan faces a "very real risk of mass atrocities" and that peacekeepers would be powerless to stop such a bloodbath.

The conflict has killed tens of thousands of people and displaced more than 2.5 million, but UN diplomats expect the crisis to worsen.

South Sudan won independence from Sudan in 2011 with strong support from the United States.

The United States is pushing for an arms embargo and sanctions, but Russia and China are opposed to such measures.