(IDEX Online) - De Beers has reportedly raised rough diamond prices by as much as five per cent at its first Sight of 2020.Insiders indicate that most of the increases affect stones over one carat, according to a Bloomberg news report. The scale of the price hike, described as the biggest in years, has surprised many within the industry. De Beers dropped its prices and started offering discounts and extra flexibility to Sight holders in August.It reportedly increased put them up again by two or three per cent at an extended Sight in December as demand began to firm, and has now followed through with further rises at its ongoing Sight 1, which concludes in Gabarone, Botswana, on Friday.De Beers sold $440m of rough in December, the fourth consecutive month in which 2020 Sights matched or surpassed their 2019 equivalents.De Beers does not comment on prices.