International aid bodies said on Saturday they pulled their staff out of South Sudan's northern Unity State owning to the escalating clashes between government forces and the rebels.

In a statement on Saturday, the Medicine Sans Frontiers (MSF) said "it has been forced to withdraw its international staff and halt all medical services at Leer hospital due to heavy fighting in Unity State."

"We withdraw again with a heavy heart, because we know how civilians will suffer when they are cut off from critical, life-saving medical care," said Paul Critchley, MSF mission head in South Sudan, in the statement.

Also on Saturday, the International Committee of the Red Cross (ICRC) announced a similar decision to pull out of the country.

The ICRC expressed concerns over the safety of thousands of the civilians fleeing the fighting in the Unity State.

According to the United Nations, around 100,000 people have been uprooted last week due to renewed clashes in South Sudan.

South Sudan, which only became independent in 2011, plunged into violence in December 2013, when fighting erupted between troops loyal to President Salva Kiir and defectors head by his former deputy Riek Machar.

The conflict soon turned into an all-out war, with the violence taking on an ethnic dimension that pitted the president's Dinka tribe against Machar's Nuer ethnic group.

The clashes have left thousands of South Sudanese dead and forced around 1.9 million people to flee their homes.