Former president Robert Mugabe has been told to appear before a parliamentary committee on May 9 to give information on the alleged disappearance of diamond revenue while he was in power, a state newspaper said on Friday.The mines committee wants Mugabe to answer questions over his claim two years ago that Zimbabwe had lost out on up to $15 billion worth of earnings.Evidence needed"We have set May 9 as the date on which (Mugabe) will give evidence," the committee’s chairperson, Temba Mliswa, told The Herald. "It is a resolution that we made long ago, but we first wanted to receive evidence from other State institutions to determine whether it is necessary or not to invite him. After gathering all evidence, it was the committee’s view that we call the former head of state and government," Mliswa said.Joint venturesFormer vice president Joice Mujuru will also be summoned, the Herald said.The committee has so far heard evidence from top mining executives, as well as former and serving security officials. Some told the committee that Zimbabwe's police and intelligence agencies were at one point funded through joint diamond mining ventures, a report by Source said. Figure 'wasn't factual'Commentators say the figure of $15 billion is unrealistic. Mugabe himself told the private Zimbabwe Independent newspaper recently the figure wasn’t factual."I was given that (figure) by some officials, that figure had been circulating around, but really it was not confirmed; it was just a story," he was quoted as saying.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.