Fighting between rebels and government forces in South Sudan, which had eased since May, resumed Sunday and has continued through the week as the two sides battled over control of Nasir, a town about 300 miles north of the capital Juba, Al Jazeera reported Monday.

The attack on Nasir is “the most serious resumption of hostilities” since the May ceasefire, the United Nations Mission in South Sudan, or UNMISS, said in a statement released Sunday. While the rebels reportedly claimed that they had seized the town in self-defense, government forces denied that the town had fallen.

Fighting has been raging in South Sudan -- the world’s newest country -- since December 2013 when President Salva Kiir accused former Vice President Riek Machar of plotting a coup to overthrow the government.

The ensuing political infighting later intensified into a full-fledged civil war between the rebel army, led by Machar, and government forces. According to the U.N., more than 1.5 million civilians have been forced to flee conflict-ridden parts of the country while more than seven million people are now “at risk of hunger and disease.”

south sudan map 2 More than 1.5 million civilians have been uprooted in South Sudan while about 7 million are now at risk of hunger and disease. Photo: OCHA/ReliefWeb

Marie Harf, the deputy spokesperson for the U.S. State Department, condemned the attack in a statement released Monday, stating that the civilians in South Sudan had “suffered from frequent and horrific acts of violence and human rights abuses since fighting broke out in mid-December.”

Warning that there were “famine conditions” looming in many areas of the country, Harf urged both parties to “recommit themselves to inclusive political negotiations and to reaffirm their commitment to the Cessation of Hostilities Agreement,” referring to a January pact signed by the rebels and government forces.

Kiir and rebel leader Machar had met in May and again in June to recommit to the pact. However, it has failed to prevent the steady eruptions of violence in the impoverished country.