05/09/2015 11:16 EDT | Updated 05/09/2016 05:59 EDT

Aid agencies withdraw international staff from town of Leer in South Sudan fearing violence

JUBA, South Sudan - Two global aid agencies Saturday evacuated their international staff from a part of war-torn South Sudan fearing clashes between the rebels and government troops.

Doctors Without Borders and the International Committee of the Red Cross both said that they withdrew their international staff from the rebel-held town of Leer in the south of oil-rich Unity State. A statement from Doctors Without Borders said the organization is "gravely concerned about an imminent attack" on Leer, and that they have been forced to halt all their medical services at Leer hospital.

U.N.'s humanitarian co-ordinator for South Sudan Toby Lanzer said Friday that 100,000 people have been displaced from their homes due to fighting over the last week in the south of Unity State.

Leer is the hometown of South Sudan's rebel leader Riek Machar. South Sudan descended into conflict in mid-December 2013 when troops loyal to former vice-president Machar clashed with those loyal to President Salva Kiir in what government claimed was a coup attempt. Tens of thousands of people have died and two million have been displaced since the conflict began, according to the U.N.

In January 2014, troops allied to the government swept through Leer and devastated the town, leaving behind dead civilians and forcing aid workers and civilians to flee into swamps for survival.

"We must sound the alarm on the grim situation in southern Unity State," said Pete Buth, deputy operations director for Doctors Without Borders. "We cannot stand by and watch as civilians and medical facilities are attacked again."

"Today, we withdraw again with a heavy heart, because we know how civilians will suffer when they are cut off from critical, lifesaving medical care," said Paul Critchley, head of mission of Doctors Without Borders. "We call on all armed actors to show unconditional respect for our patients, medical facilities and staff."

Government checkpoints and bad roads have prevented aid workers and U.N. staff including human rights monitors from reaching areas affected by the fighting, said U.N. Spokesman Joe Contreras.

Government forces in various parts of South Sudan have been gaining ground against the rebels since the collapse of peace talks in early March.