John Aurelio, Deputy Secretary-General of the South Sudanese opposition party United Democratic Front (UDF), said they lost communication with their chairman Peter Abdel-Rahman Sule for more than a month.
Sule, a lawyer and politician, has been missing since 24 July 2015, according to relatives.
Aurelio told Radio Tamazuj that they cannot confirm whether Sule has been killed or not. He said Sule was reported missing in Uganda last month and has not been found.
Aurelio further said his boss sought asylum in Uganda after South Sudan’s government threatened to kill him. He said his leader decided to leave Juba after the government took his passport and prevented him from travelling to peace talks in Addis Ababa.
The UDF member said they cannot accuse the government of assassinating him in Uganda.
He called upon the international community to exert efforts to find Sule. He also called the Ugandan authorities to tell his family and his party about his whereabouts.