At least 18 people were killed in clashes between South Sudanese government troops and rebels loyal to former deputy president Riek Machar, authorities said yesterday. The attack came on Saturday night in the war-torn nation's Upper Nile region.

"The raid on the army base in Latjor state left eight soldiers and 10 attackers dead," deputy military spokesman Santo Domic Chol told DPA.

Rebel spokesman Paul Gabriel Lam told dpa his forces were responding to government attacks on their positions.

Last week, South Sudan's President Salva Kiir declared a state of emergency in another area, Lakes state, after days of tribal clashes that left almost 100 dead.

South Sudan plunged into civil war in December 2013 when a political crisis escalated into fighting between forces loyal to Kiir, an ethnic Dinka, and rebels allied with his former deputy Riek Machar, a Nuer. The war entered its fourth year last week, with over 4.8 million people in South Sudan facing severe food shortages, according to aid agencies.

The conflict has reopened ethnic fault lines and spread across the country, where more than a dozen armed groups are battling for land, resources, revenge, and power amid widespread reports of rape, murder and torture. Several ceasefires have been agreed but broken. Tens of thousands have been killed since the war broke out.