Several senior government officials have reportedly been summoned by Zimbabwe's parliamentary portfolio committee on mines and energy over the missing $15 billion diamond revenue.According to reports, ex-president Robert Mugabe, announced in 2015 that $15bn of diamonds were spirited out of Marange, the dusty fields more than four hours' drive from the capital Harare which were the site of a bloody military clampdown in 2008.The privately owned NewsDay newspaperreported that the mines and energy portfolio committee which was chaired by independent lawmaker, Temba Mliswa, had summoned Vice President Kembo Mohadi – a state security minister at the time - finance minister Patrick Chinamasa and former police boss Augustine Chihuri to give evidence before it. Other senior officials who were summoned to appear before the commission were the current Police Commissioner-General Godwin Matanga, home affairs ministry secretary, Melusi Matshiya, and his defence counterpart, Martin Rushwaya. The state owned Herald newspaper said that former defence minister Sydney Sekeramayi, ex-presidential affairs minister Didymus Mutase were also among those who had been summoned. 'No evidence to back Mugabe's claim' The committee's chairperson last month also told NewZimbabwe.com that Mugabe was also expected to be summoned to give evidence before the mines commission.KEEP UPDATED on the latest news from around the continent by subscribing to our FREE newsletter, Hello Africa.FOLLOW News24 Africa on Twitter and Facebook. Mliswa, however, indicated that although the high ranking former and present government officials were expected to appear before the committee, it did not mean they were guilty of looting the funds. "We're not saying that they are guilty, but we would like to find out whether they knew about the concessions and who was running the concessions because all this information is very necessary," Mliswa was quoted as saying. This came amid reports that independent researchers had cast doubt on Mugabe's $15 billion figure.Zimbabwe journalist Nelson Banya said in a piece for ZimFact in March that there was 'no evidence to back up Mugabe's claim, which had been taken up and repeated by media, politicians and civil society groups.'Wrote Banya: "To reach the level of earnings claimed by Mugabe.... Zimbabwe would have produced an average 40 million carats annually, output which could not go unnoticed in the industry, given its impact on global supply."