President Salva Kiir says at least 30 people have been killed in fighting in Nasir on Sunday.
The military spokesman of the SPLA in Opposition, Lul Koang Ruai confirmed the fighting.
He said the government troops were trying to expand the area under their control, leading to the fighting.
The president called for an end to the fighting.
He spoke at Juba airport on arrival from a trip to America.
The President said there was fighting in the morning and another in the evening.
“In these two attacks, 37 soldiers were killed on their side and all of them are our people and Riek Machar just wants to play with people,” said Mr President.
“I want to tell all of you that not accept fighting .We are here for peace.”