Euro zone inflationary pressures are at a four-year high, suggesting the European Central Bank's trillion-euro bond-buying program is working, an indicator designed to predict cyclical trends showed on Thursday.

The Eurozone Future Inflation Gauge (EZFIG), a measure of the outlook for inflation published by the Economic Cycle Research Institute, rose to 100.4 in May from April's 100.2.

"Euro zone inflation continues to be in an uptrend. With the EZFIG increasing further to a four-year high in May, euro zone inflation pressures continue to build," said Lakshman Achuthan, ECRI's chief operations officer.

Inflation softened in the bloc during June to 0.2 percent year-on-year, moving away from the European Central Bank's target of close to 2 percent, official data showed on Tuesday