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The British pound was down 0.3 percent $1.5956, with a Swiss account cited to be a seller in afternoon trade. Sterling was also sold against the euro, the Australian and Canadian dollars.
This earlier dragged sterling trade-weighted index to to a nine-month low, Bank of England data showed.
Sentiment towards the pound has also been hurt by uncertainty over Britain's relationship with the European Union.
Prime Minister David Cameron will give a closely watched speech about Europe on Friday, following calls from some in his own party for a referendum on whether Britain should exit the EU.