(IDEX Online) - A parcel of diamonds seized three years ago from UK-listed miner Petra has been declared property of Tanzania's government.It has nationalized the shipment, now said to be worth $29.5m, after a court ruled that two former government employees had deliberately undervalued the gems, which were destined for Antwerp, according to a report on Turkey's state-run Anadolu news agency.Tanzania's government is battling corruption and the theft of mineral resources in the country and has passed laws raising mining taxes and forcing companies to renegotiate contracts.The 71,654 carats of diamonds, originally valued at $15m, were seized at Julius Nyerere International Airport, Dar es-Salaam, in 2017.Petra - which is a quarter-owned by the Tanzania government - said at the time that it was not responsible for the pre-export valuation of diamonds from its Williamson mine (pictured) - a task it says was carried out by the government's diamonds and gemstones valuation agency.