It is not clear what triggered the clashes although sections of the border have long been contested.

At least four members of the South Sudanese security forces have been killed in fighting with the Ugandan army near the countries’ shared border, according to local officials, as tensions flare over disputed border demarcations.

Three South Sudanese soldiers were shot dead on Monday by Ugandan forces who retaliated after one of their soldiers was killed, Major General Felix Kulayigye, spokesperson for the Ugandan military, said on Wednesday. But Wani Jackson Mule, a local official in South Sudan’s Central Equatoria state, said he received the bodies of five soldiers.

Uganda has a history of involvement in South Sudan and has long provided military support to President Salva Kiir, including a deployment of special forces since March.

A spokesman for South Sudan’s military, Major General Lul Ruai Koang, said on Wednesday that military leaders from South Sudan and Uganda have agreed to an immediate ceasefire to enable an investigation of the latest border clash.