JOHANNESBURG (Reuters) - South Africa's former president Jacob Zuma is exploring every legal avenue after being given a 15-month jail sentence for defying an order to appear at a corruption inquiry, a senior official in the African National Congress (ANC) said on Tuesday.

       "President Zuma is exploring every legal avenue that is available to reduce or to remove the custodial sentence. ... We believe that the judiciary must be left to make its own decisions, (but) ... we would hope that comrade Zuma's court application will be successful," the party's Deputy Secretary General Jessie Duarte told a news conference.

       Zuma's lawyers will approach the high court later on Tuesday to try to block his arrest in the wake of last week's constitutional court sentence.

       (Reporting by Alexander Winning and Wendell Roelf; Editing by Promit Mukherjee)