Powell is scheduled to give his semi-annual monetary policy testimony to Congress at 1400 GMT, and investors see a worrying lack of inflation globally as one reason for Powell to sound suitably dovish.

The pan-European shares index fell 0.2% and was on course to extend losses to a fourth day, with Spain's IBEX  underperforming with a 0.4% loss.

Stocks with exposure to Mexico led losses in Madrid with BBVA, Iberdrola and Telefonica down between 0.6% and 0.8%, after a shock resignation of Mexican Finance Minister Carlos Urzua on Tuesday rattled Mexican markets.