At least 10 people were killed in the South Sudanese town of Wau on Monday, as ethnic militias went house to house searching for people from other groups, witnesses said.

Streets were deserted as families hid inside, residents told Reuters by phone. Some reported seeing killings.

Witnesses said the militias were aligned with the government's side in the country's ethnically-charged civil war. They accused army soldiers of blocking the main road to a civilian encampment protected by U.N. peacekeepers.

South Sudan's deputy army spokesperson, Colonel Santo Domic Chol, said fighting had first broken out during a mutiny by soldiers at the town's prison. He was awaiting more information, he said.

The fighting followed an ambush that killed a brigadier general and a colonel in Wau state over the weekend, a rebel spokesman based outside the country said.

"This morning the government forces were retaliating against innocent Fertit people," he said, referring to a local ethnic group.

South Sudan descended into civil war in 2013 after President Salva Kiir, a Dinka, fired his deputy, Riek Machar, a Nuer. Fighting since then has often split the oil-producing country along ethnic lines and created a patchwork of armed factions.