The United Nations and African Union on Tuesday called on South Sudan's warring parties to take concrete steps to implement the latest peace deal signed last month.Civil war in the world's youngest country erupted in December 2013 and uprooted 4.2 million people - roughly a third of the population."We are looking forward to further improvement in the security situation and other positive signals that can generate confidence and mobilisation from the international community," Jean Pierre Lacroix, the UN Under Secretary for Peacekeeping Operations, told reporters, winding up a three-day visit.Lacroix visited the country with the African Union Commissioner for Peace, Smail Chergui. He went to UN-run camps for the displaced in Bentiu hosting 114 000 people.South Sudan's warring sides signed a permanent peace agreement on September 12. A US-funded survey released recently estimated that nearly 400 000 people have been killed in the conflict."The partners of South Sudan are keen to see a few things materialise particularly the full cessation of hostilities," Lacroix said."Parties themselves (need to) take the lead in advancing the peace process."The African Union's Chergui issued a vague warning."Let's just take note today that everybody wants to implement that agreement faithfully and we will hold accountable anyone going the other road," he said.South Sudan broke away from Sudan in 2011 after a long and bloody independence struggle.But just two years later, war broke out, triggering a severe humanitarian crisis.A struggle for power between President Salva Kiir, a member of the Dinka tribe, and rebel leader and former vice president Riek Machar, a Nuer, meant the conflict quickly took on an ethnic character with civilians subjected to massacres and widespread rape by forces on both sides. Under the new peace deal, Kiir remains president while Machar wins back his old post of deputy.Tens of thousands of people have been killed and millions pushed to the brink of starvation or forced to flee their homes in one of the world's worst humanitarian crises.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.