By Todd Buell in Frankfurt and Paul Hannon in London 

FRANKFURT--European Central Bank President Mario Draghi on Thursday indicated that the bank stands ready to expand its stimulus programs and projected slower-than-expected economic growth in the eurozone, as well as lower inflation rates. as a result of the slowdown in some large developing economies.

In a news conference, Mr. Draghi stressed the central bank's "willingness and ability to act if warranted," suggesting the ECB could broaden its stimulus programs to ensure inflation rises to a target rate of just under 2%.

Mr. Draghi said an "interim evaluation" of the impact of recent turbulence in global financial markets and signs of a slowdown in China, points to "continued, though somewhat weaker economic recovery, and a slower increase in inflation rates compared with recent expectations."

However, he added that while the "downside risks" to growth and inflation have increased, it was possible recent developments would be "mainly transitory."

Earlier Thursday, the ECB left its main policy rate for its regular loans to banks at 0.05%. It also left its deposit rate, the rate it pays for banks to park excess funds overnight, at minus 0.20%, meaning that banks continue to pay to park cash with the ECB.

Since March, the ECB has purchased EUR60 billion ($68 billion) a month in mostly government bonds in an effort to revive inflation and growth in the currency bloc by adding to the money supply. The program is intended to run through September 2016, or until inflation is back to target.

Recent data on bank lending to households and companies suggest the ECB's stimulus is starting to find its way into the economy. But there is concern that QE isn't doing enough to bring inflation back to the ECB's medium-term target of just below 2%.

The most recent data, published Monday, showed annual inflation in the currency bloc at only 0.2% in August.

Lower energy prices and upward pressure on the euro, stemming from uncertainty about the timing of rate rises in the U.S., are keeping consumer price pressures subdued. Meanwhile, signs of slowing in China have raised concerns that European exports may not be as strong as expected.

The ECB's economists lowered their forecasts for inflation over coming years, and indication that policy makers may have to expand their bond buying program if they are to succeed in raising the inflation rate to their target.

The economists now expect an inflation rate of 0.1% in 2015, 1.1% in 2016 and 1.7% in 2017. In June, they forecast a rate of 1.8% in 2017, up from 1.5% in 2016 and 0.3% this year.

Write to Todd Buell at todd.buell@wsj.com and Paul Hannon at paul.hannon@wsj.com

(END) Dow Jones Newswires

September 03, 2015 09:33 ET (13:33 GMT)