Thousands of civilians fled Akobo, an opposition-held town in eastern South Sudan, after the army issued an urgent evacuation order.
The exodus began Saturday night, as women, children, and the elderly crossed into Ethiopia, leaving the town nearly empty, officials said.
Fighting has already reached areas west of Akobo, with residents reporting the ominous sounds of approaching machine guns on Sunday evening.
The South Sudan People’s Defense Forces ordered the U.N. Mission in South Sudan to close its Akobo base on Friday.
Humanitarian groups and civilians were instructed to leave to “avoid unnecessary collateral damage” before a military operation targeting the town and surrounding areas.
Akobo has been one of the last strongholds of the SPLM-IO, led by detained Vice President Riek Machar, a key opposition figure.
The 2018 peace deal between Machar and President Salva Kiir has nearly collapsed amid renewed fighting that began last year.
Northern Jonglei has seen intensified confrontations since December, displacing more than 280,000 people after government forces repelled opposition advances.
Akobo, under opposition control since the 2013 civil war, had been a refuge for over 82,000 displaced people, partly due to U.N. peacekeepers.
UNMISS has not officially responded to the government’s evacuation order, while two U.N. flights removed most humanitarian staff on Sunday.
The International Committee of the Red Cross continues to operate a surgical unit at Akobo County Hospital despite fears of imminent assault.
Local health officials expressed concern for patients, citing insufficient fuel to safely relocate wounded civilians amid escalating military threats.
On Saturday, residents demonstrated near the U.N. base, calling for peace and protection, defying the army’s ultimatum with a peaceful march.