Botswana will take a 24% stake in Belgian diamond trader HB Antwerp in a challenge to a decades old arrangement with De Beers, the world’s biggest diamond company.

The country’s state gem trader will also supply HB with the precious stones for five years, President Mokgweetsi Masisi said at an event at HB’s premises in Gaborone, the capital, on Monday.

Botswana is currently negotiating a new agreement with De Beers under which most of the country’s gems are mined by a joint venture with the government and sold by De Beers. Masisi has threatened to walk away from the talks and has praised how HB handles diamonds extracted at the Karowe Mine, which is owned by Lucara Diamond Corp.