Gaborone: The value of rough diamonds exports from Botswana’s mines fell 15 percent in the first six months of the year to $1.7 billion, official data showed on Tuesday.

Diamond exports contribute 30 percent to the GDP of the southern African nation. But diamond demand has slowed since late 2014 as middlemen who buy rough stones struggle with a stronger dollar and liquidity problems.

The bulk of Botswana’s diamond exports are from Debswana, a joint venture between the government and diamond giant De Beers. Debswana’s output slid 4 percent to 12 million carats in the first six months of this year.