ABA, Democratic Republic of Congo — As diplomats began another round of peace talks over the civil war in South Sudan, the country’s military forces captured a rebel headquarters, further weakening the fractured rebel movement and prompting a mobilization of soldiers in a neighboring nation.
South Sudan’s army marched Sunday night into the town of Lasu in the country’s southwest, near the border of the Democratic Republic of Congo. The city fell on Monday, according to refugees who fled the fighting.
Lasu was the southern headquarters of the country’s major rebel group, the SPLA-IO, after the fall of its main base in the country’s northeast this summer.
Ateny Wek Ateny, a spokesman for President Salva Kiir of South Sudan, insisted that the government was adhering to the unilateral cease-fire that Mr. Kiir had declared in May.
“Lasu is under government control; it has never been under rebel control,” said Mr. Ateny, while acknowledging that rebels were active in the area. “Therefore, the government cannot attack its own territory.” A report released this week by the government’s Cabinet Affairs Ministry, however, said the town had been under rebel control.
Refugees who have fled the town say gunshots continued throughout Tuesday. Smoke billowed from a village near the border, and the Congolese military deployed troops to prevent armed combatants from crossing into its territory, it said.
South Sudan’s war began in December 2013, pitting troops loyal to Mr. Kiir, an ethnic Dinka, against rebels led by former Vice President Riek Machar, an ethnic Nuer, in fighting that often falls along ethnic lines. The two men signed a peace deal in 2015, but it lasted barely a year.
Tens of thousands have been killed in the past four years, and more than two million people have fled the country for neighboring Uganda or the Democratic Republic of Congo, the largest national exodus in Africa in 20 years.
This week, another round of regionally brokered peace talks began in Ethiopia. Since last year’s peace deal, Mr. Kiir’s army has solidified its hold on the country, while the rebels have splintered into competing factions and struggled to gain significant arms supplies.
“The government thinks it is winning the war,” said Alan Boswell, an independent South Sudan researcher. “The opposition sees no reason to join a government that won’t concede any power. It’s very difficult to bridge those two positions.”
More than 300 families have entered the sleepy border town of Aba in the Democratic Republic of Congo since Sunday, according to local officials.
On Tuesday, dozens of people sheltered in a dilapidated church near the border as dark smoke billowed behind them in South Sudan.
Inside the church, Cecelia Senye said she had been boiling maize meal in a village near Lasu when shooting began Sunday night. She left her pot burning on the fire as she grabbed her children and fled through the forest.
“I was only thinking: get to Congo,” she said.
Other families were not as lucky.
William Ayambo, 53, who reached Aba on Monday, was in Lasu’s town center when the attack began. He ran to his house to find his wife and five children, but they were gone. He has not found his family.
“They are all missing,” he said.
The latest round of fighting is the government’s third offensive since late October. The army also took a strategic enclave on the Ugandan border and pushed into rebel areas west of Juba.
“The government can win on the ground, but it’s increasingly empty ground,” said Alex Rondos, the European Union’s special representative to the Horn of Africa. “You extended your territory, but that is politically meaningless.”