BAMAKO, Aug 26 (Reuters) - Mali"s former prime minister Boubeye Maiga was arrested on Thursday for his role in the purchase of a presidential plane during the rule of ousted President Ibrahim Boubacar Keita, his lawyer said. The exact reason for the arrest was not clear, but it was related to Mali"s purchase of a jet in 2014 for $40 million, his lawyer, Kassoum Tapo, said by phone, without giving further detail. "We have not seen the case file and until then we cannot speak further," he said. The Justice Ministry did not respond to a request for comment. Critics at the time claimed that the Keita administration overpaid and that the deal was corrupt. It led to a political scandal that hurt Keita"s presidency and spooked lenders. The International Monetary Fund and the World Bank froze financing to the West African country as a result. It was not clear what evidence prosecutors have against Maiga or why he was arrested now. He served as prime minister from 2017-2019 and is seen as a possible candidate in the presidential vote that interim authorities promise to hold next year following Keita"s ouster as president last August. The transition is being led by Assimi Goita, the Malian colonel who led the coup and is now interim president.