The UN peacekeeping force in

The attackers struck late Wednesday on a temporary base operated by Ghanian forces for the United Nations Mission in South Sudan (UNMISS), next to a camp for people displaced by the country's civil war.

UNMISS said in a statement the attack had been "carried out with callous disregard for the lives of civilians as well as UN and humanitarian workers".

It said it had not identified the attackers, but that they fired from the direction of the nearby town of Leer, which is held by the government. There were no reported victims.

"We strongly condemn the attack, and call on all parties to the conflict to respect the sanctity of UN premises,"David Shearer, the head of the mission, said in a statement.

The area has long been riven by fighting between forces loyal to President Salwa Kiir and those who support his former deputy Riek Machar.

Aid groups have denounced a "man-made" famine caused by the conflict that has forced at least 1.7 million people to flee the country.

"The people are hungry and deprived as the result of the famine. However, it is clear the attackers have no consideration for their plight," Shearer said.

He added that an inquiry was underway, which would determine if UNMISS would reinforce the base at Leer.