Copper prices fell on Tuesday for the first time in nine days on signs that China’s State Reserve Bureau, which is reputed to be carrying a giant short position that it needs to cover by next month, has stretched out to two years the period over which it can deliver the metal.

The bureau manages China’s strategic commodities holdings. Speculation that it has built up a short position of 100,000-200,000 tonnes has driven copper prices to record levels this month. The trades were supposedly carried out by Liu Qibing, a bureau official who has since disappeared from the market.