Egypt's pound weakened to 7.29 per dollar at an unscheduled central bank auction on Tuesday, from 7.24 a day earlier, the weakest it has been allowed to reach since auctions began in December 2012 and the third depreciation this week.

The bank offered 40 million dollars and sold 38.4 million at a cutoff price of 7.29 pounds per dollar, the central bank said.

The rates at which banks are allowed to trade dollars are determined by the results of central bank sales, giving the bank effective control over official exchange rates, though there remains an active black market in the pound.

The bank usually only holds dollar auctions on Sunday, Monday, Wednesday and Thursday.