The Bank of England's deputy governor for financial stability has voiced concerns over how financial markets will react to an interest rate rise by the US Fed.
Sir John Cunliffe told the Guardian that global financial markets are "quite fragile" due to a lack of liquidity which can make it more difficult for traders to exit some positions.
"People seem to be under-pricing liquidity. We don't know how [the markets] will behave under stress and we are watching that very carefully," he said before making a speech at a dinner held by campaign group The CityUK.
"If and when US interest rates go up ... there are concerns about how the market will adjust. This must be the most advertised, well signalled change in monetary policy in the history of man."
"Nonetheless you don't know. These are different sorts of markets to the ones we had before."
Some economists have said the Federal Reserve could start raising rates as soon as September. A statement due out this evening is expected to shed more light on this.