A committee of lawmakers in Zimbabwe is to summon former president Robert Mugabe to testify at a probe into lost revenue from diamond mining, a legislator said on Tuesday.The lawmakers plan to question Mugabe over his 2016 claim that the country had lost $15bn in income from diamonds due to corruption and foreign exploitation.Mugabe - whose own regime was accused of siphoning off diamond profits - was ousted last November after a military takeover that ushered his former deputy, Emmerson Mnangagwa, to power."The committee resolved to call the former president to testify," Temba Mliswa, an independent lawmaker who chairs parliament's committee on mines and energy, told AFP."He was the president, and we want to know where he was getting the $15bn figure (from)."He said no date had yet been set to call Mugabe to testify.It was unclear whether Mugabe, 94, who has not been seen in public since his ousting, could be forced to face a grilling from lawmakers.Mugabe ruled the country for 38 years, exercising ruthless control over parliament, security forces and the country's mineral resources.The committee has already summoned former ministers, ex-police chiefs and heads of several government department.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERMliswa said a report would be compiled when the investigation was complete.Zimbabwe discovered alluvial diamonds in Chiadzwa, in the east of the country, over a decade ago, and rights groups have accused security forces of using brutal methods to control the scattered deposits.Over 200 people were killed during operations to remove illegal panners from the area, rights groups say.Amid allegations of massive looting, Zimbabwe allowed several diamond companies to mine the area - most of them as joint ventures between the government and Chinese firms.FOLLOW News24 Africa on Twitter and Facebook.