German central bank chief Joachim Nagel told CNBC on Friday that any potential move by the European Central Bank (ECB) to hike interest rates into restrictive territory would be "very much dependent on how the energy prices evolve." Nagel's comments come a day after the ECB raised its key interest rate by a quarter percentage point to 2.5%. He noted that rates are currently at the upper end of neutral territory but did not rule out the need to enter a "mild restrictive territory."