Africa focused diamond producer Petra Diamonds said annual output increased five fold to over 1m carats while sales declined and trading conditions remained challenging.Production for the year ended 30 June 2009 rose to 1.1m carats an increase of over 453.6% from the same time a year earlier. Revenue however fell $69.1m during the period from $76.9m as rough diamond prices fell. "Cautious optimism is at the forefront of Petra's thinking and, while we remain aware that a softening in prices is possible, we expect prices to continue to slowly and gradually strengthen," Petra said in a company statement. While trading conditions remain challenging, "our cash flow remains tight, with the recent strengthening of the rand absorbing much of the benefit of the increase in rough prices," added chief executive Johan Dippenaar.