LONDON, July 7 (Reuters) - Petra Diamonds Ltd (PDL.L) said on Tuesday 7 July its annual output jumped above 1 million carats, but the African diamond producer added that revenue dipped and trading conditions remained challenging.

Petra Diamonds CEO Johann Dippenaar holding a 26.58 carat rough blue diamond - Photo: www.petradiamonds.com

Annual production surged to 1.1 million carats in the year to end June, up more than 450 percent from the year earlier, but revenue fell to $69.1 million from $76.9 million on lower rough diamond prices.

"Trading conditions remain challenging and our cash flow remains tight, with the recent strengthening of the rand absorbing much of the benefit of the increase in rough prices," said Chief Executive Johan Dippenaar.

(Reporting by Julie Crust; Editing by Matt Scuffham)