The project, known as Cut 9, follows a $3 billion (£2.33 billion) expansion of Botswana's richest diamond mine in 2010 to uncover 100 million carats of diamond and extend the life of the mine to 2024.

"Cut 9 will be a huge investment by De Beers as it will require a significant capital outlay," mines minister Sadique Kebonang said late on Tuesday. "We should be able to start Cut 9 in the next two to three years."

Debswana owns three other diamond mines in the country, one of which was placed under care and maintenance at the beginning of 2016.

Kebonang also said his government and De Beers have also started talks about the extension of their ten-year marketing and sales agreement, which is due to lapse in 2020.

Under the agreement signed in 2010, De Beers shifted more than $6 billion of annual rough diamond sales from London to a Gaborone-based joint venture called DTC to sort, value and sell diamonds to the global market.

(Writing by Tiisetso Motsoeneng, editing by Louise Heavens)