An East African regional bloc says one of its officials monitoring a cease-fire in South Sudan died while being held by rebel fighters.

The regional bloc, IGAD, said the monitors had landed in Unity state Sunday for a routine inspection mission before being arrested.

Seyoum Mesfin, the chair of the IGAD team, said those responsible for the death "will bear consequences." But a security report about the incident seen by The Associated Press said the death — of a man representing South Sudan's government — was from natural causes.

Rebels loyal to South Sudan's former vice president have been fighting government forces since December. Thousands of people have been killed in the fighting and more than 1 million have fled their homes. The country also faces a mass hunger crisis.