Six aid workers are missing in South Sudan after clashes broke out Sunday evening between government and opposition soldiers near the northwestern town of Raga.

The government blames the opposition forces, known as IO, loyal to former Vice President Riek Machar for the abductions.

"This kind of behavior is unbecoming," said government spokesman, Ateny Wek Ateny, who demanded the release of the aid workers.

The missing humanitarian workers are from three organizations, two international groups, HealthNet and Solidarity International, and one local aid group. Solidarity International's country director, Mainul Islam Opu from Bangladesh, is the only foreigner among the victims, the rest are South Sudanese nationals.

South Sudan's opposition group, IO, confirmed that they have four of the aid workers but said they rescued the aid workers from being used as "human shields" by the government.

"They are currently safe and sound with our forces around Raga and will be handed over to the concerned third party as soon as possible," opposition spokesman Col. Lam Paul Gabriel told The Associated Press. Gabriel said they found the aid workers when fighting a government-allied militia during which they killed 35 militia fighters between the towns of Wau and Raga in Western Bahr el Ghazal state.

A statement put out by the local government of Raga said that two humanitarian cars were burned to the ground at the scene.

The fighting comes while high-level peace talks have started in Ethiopia, which are aimed at bringing peace to the war-torn South Sudan.

At least 95 aid workers have been killed in South Sudan since the start of the civil war in 2013, including 28 so far in 2017, said the U.N. Last month six aid workers were killed in a single attack in Duk County in Jonglei State.