U.S. Secretary of State John Kerry placed a call to South Sudan Prime Minister Salva Kiir Mayardit, urging him to form a new government \"quickly and transparently in a manner that respects South Sudan\'s Transitional Constitution, and in a way that also reflects the diversity of its people.\" Earlier this week, Kiir fired his vice-president and 28 of his cabinet ministers. In a read-out of the call released by the State Department on Saturday, Kerry reiterated \"the United States\' concerns about the political situation in Juba, as well as the deeply disturbing violence and worsening humanitarian crisis in Jonglei State.\" Jonglei is located in the east of South Sudan, and is the poorest of all 10 states in the country. It is home to some six different ethnic groups but inter-communal violence is widespread, even spurring militants with ties to Khartoum since the Sudanese civil war. At least 100,000 people have been internally displaced due to the fighting, and they are in desperate need of water, food and shelter. Kerry encouraged Kiir to \"act expeditiously to protect civilians, end human rights violations, and take urgent steps to cease ethnically motivated violence.\" \"Those responsible for human rights violations and attacks on civilians - including members of the Sudan People\'s Liberation Army - must be held accountable,\" said Kerry. \"Lifesaving humanitarian assistance must be allowed to reach the estimated 100,000 civilians affected by the fighting,\" he stressed. He added that \"the world is watching\" to find out whether South Sudan - the world\'s youngest nation at only two years old - will go down the path of \"peace and prosperity\" or \"the tragic path of violence and conflict.\"