KUALA LUMPUR (Reuters) - A senior Malaysian opposition leader was detained by anti-corruption authorities on Thursday, a source said, as part of a nationwide campaign against graft launched by Prime Minister Najib Razak. Hundreds of people including many high-profile figures have been arrested this year by the Malaysian Anti Corruption Commission (MACC), at a time when a multi-billion dollar scandal involving state fund 1Malaysia Development Berhad (1MDB) hangs over Najib. Shafie Apdal, a former close ally of Najib, was detained at the MACC office in the state of Sabah in connection with a RM1.5 billion ($355 million) embezzlement probe, according to a source in the anti-graft agency. The investigation covers alleged corruption involving projects doled out by the federal government through the Rural and Regional Development Ministry between 2009 and 2015, when it was run by Shafie.  He will be brought before a magistrate for a remand hearing tomorrow,  said the source, who was not authorized to issue statements on behalf of the MACC. Shafie could not be contacted. Darell Leiking, Deputy President of his Parti Warisan Sabah party, described the arrest as political persecution.  We shall ensure that we shall fight for justice for all those who this (Najib) regime intends to suppress and intimidate,  Darell told Reuters. Prior to Shafie s arrest, the anti-graft agency detained two of his brothers and several senior Warisan leaders. Shafie, a former vice-president of Najib s ruling United Malay National Organisation (UMNO), quit the party after he was suspended for questioning the prime minister over his handling of the 1MDB scandal. He later founded Warisan to run for office in his home state. Over the past two years, Najib has grappled with the 1MDB scandal which has been the subject of investigations in at least six countries for money-laundering and misappropriation of funds. Malaysia s attorney-general closed the 1MDB probe in January 2016, and cleared Najib of any wrongdoing.  