The United Nations Mission in South Sudan said on Wednesday it was gravely concerned about the reported execution of four rebels in the north of the country on Aug. 7.
South Sudan erupted into civil war shortly after declaring independence from Sudan in 2011, which pitted rival communities against each other and plunged the country into violence and lawlessness.
A peace agreement signed three years ago is largely holding but the transitional government has been slow to unify the various factions of the military into a single unit, write a new constitution and pave the way to elections.
The executions were allegedly in response to a July 22 attack by the South Sudan People's Movement / Army (SSPM/A) on the Mayom county commissioner, the United Nations said.
"Anyone who is suspected of a crime must be subject to a proper trial as part of a fair judicial process," the head of the U.N. mission said in a statement.
Lul Ruai, a spokesperson for the South Sudan People's Defence Forces (SSPDF), said the army had started an investigation into the killings, which it said were captured on a video.
One video shared on social media showed five men in combat fatigues shooting three hooded figures sitting on the ground.
Three men were killed by firing squad while a fourth was tied up and burned alive in a grass-thatched hut, Ruai said in a statement.
"The men were allegedly killed by elements from the SSPDF," he added.
The men were arrested across the border in Sudan on Aug. 6 and handed over to South Sudan authorities, SSPM/A spokesperson Luke Gattiek said in a statement.
(Reporting by Nairobi Newsroom Writing by Hereward Holland; Editing by Mark Potter)
