"Given the dampened price pressure, an expansive monetary policy is still appropriate in principle," Weidmann, who heads Germany's powerfull Bundesbank and has been the most outspoken critic of the ECB's policy in recent years, said at a reception in Berlin.

"But as a result of the economic recovery and a predicted inflation rate of almost 2 percent in 2019, it is quite legitimate to ask when the Governing Council should consider monetary policy normalization", Weidmann added.

The ECB Governing Council meets next Thursday in Tallinn to asses its policy stance. ECB President Mario Draghi said on Monday that the euro zone still requires substantial stimulus, even if growth in the 19-member currency bloc has improved.