A South Sudan government spokesman says that a British aid worker for the Carter Center was killed in Juba, the capital of South Sudan.

Presidential spokesman Ateny Wek Ateny said the man was entering his compound Tuesday night when gunmen shot him to death.

The British Foreign office confirmed the death of one of their citizens but provided no further information.

South Sudan has been at war since December 2013 when political divisions between President Salva Kiir and his former deputy Riek Machar spilled into widespread violence.

The U.N. says tens of thousands have been killed, and nearly 2 million are displaced, creating the world's largest single-country humanitarian effort.