"The diamond market remains weak", said RBC Capital Markets. "Clearly the market is continuing to struggle. We would argue this is in the price at these levels."

In its latest RBC Insight research the bank noted De Beers was allowing customers to defer purchases, giving midstream market players a chance to destock ahead of the holiday season later in the year.

According to the bank, this could help the downstream end of the diamond market "return to normalcy towards the end of the year", though it might not be strong enough to absorb the held-back diamonds in 2019.

That suggests continued lower sales figures, in line with figures released by Russian diamond producer Alrosa earlier this month.

On the other hand, the bank said the closure of Rio Tinto's Argyle mine would take substantial volume from the market in 2020, potentially helping prices, and De Beers outlined robust cost management in the first half of the year.

Flat diamond prices in recent times have not helped producers such as South Africa diamond miner Petra Diamonds, which recently announced plans to cut the company's costs in an effort to reduce debt. 

Anglo-American owns 85% of De Beers; the company's share price was 2,111.7p on Monday and has generally been rising since September last year when it traded at 1,475.4p.