By Tom Fairless 

A top European Central Bank official signaled on Tuesday that the ECB should soon start to wind down its EUR2.3 trillion bond-purchase program, a keenly awaited move that is expected to trigger volatility in financial markets.

"I am...optimistic that we can soon turn to the question of an exit" from easy-money policies, said Sabine Lautenschlaeger, who sits on the ECB's six-member executive board, at an event in Hamburg.

The ECB "must get ready for better times," Ms. Lautenschlaeger said.

It is the first time that an ECB board member has indicated that the days of the bank's so-called quantitative-easing program may be numbered.

Only last week, ECB President Mario Draghi said the issue of exiting the bank's controversial stimulus program hadn't even been discussed by officials at a policy meeting.

The comments come amid a surge of criticism of the ECB in Germany, where a recent jump in inflation, to 1.7% in December, has sparked political concerns over the impact on the nation's savers.

Ms. Lautenschlaeger, a former Bundesbank official who is the only German-born member of the ECB's executive board, has previously expressed skepticism about the bank's bond purchases.

She warned on Tuesday that the ECB shouldn't wait too long before starting to wind down the program.

"All preconditions for a stable rise in inflation exist," Ms. Lautenschlaeger said. The ECB shouldn't wait "until the last doubt about the return of inflation has been dispelled."

Inflation in the 19-nation eurozone jumped to 1.1% last month, the highest level in three years, due largely to a rebound in energy prices.

But it is still some way short of the ECB's target of just below 2%.

Crucially, core inflation -- stripping out volatile energy and food prices -- has remained stubbornly low.

Mindful of that gap, Mr. Draghi last week pledged to continue the ECB's bond-purchase program through the end of the year. The purchases are due to slow to EUR60 billion from EUR80 billion per month in April.

Ms. Lautenschlaeger's words indicate she may favor an end to the bond purchases before December. If so, she would be supported by her countryman Jens Weidmann, who heads Germany's Bundesbank and has opposed the QE program from the start.

German politicians and economists have been lining up in recent weeks to call for an end to the ECB's QE program, which was launched nearly two years ago and has been repeatedly expanded.

Clemens Fuest, a top German economist who is president of the Ifo economic think tank, says the ECB should start to wind down the program as soon as eurozone inflation hits 1.5%.

Ms. Lautenschlaeger warned that the risks and adverse side effects of QE were mounting the longer the program was in place.

Still, while it is "important to stop taking the medicine as soon as possible," it shouldn't be withdrawn too early, she said.

"You shouldn't abruptly stop loose monetary policy but slowly cut the dose -- such a policy has to be reduced gradually," she said.

Any formal signal that the ECB's bond-purchase program will end is expected to trigger a major repricing of financial assets, as investors price in higher future interest rates. When then Federal Reserve Chair Ben Bernanke signaled in 2013 that the Fed's own QE program would be wound down, U.S. Treasury yields surged and the dollar surged, an episode known as the Taper Tantrum.

Write to Tom Fairless at tom.fairless@wsj.com

(END) Dow Jones Newswires

January 24, 2017 14:35 ET (19:35 GMT)