Euro zone inflation unexpectedly slowed last month, adding to a string of data that points to a cooling economy.

The data will possibly make it more difficult for the European Central Bank to curb its lavish monetary stimulus later this year.  

Last month the rate slipped to an annual 1.2%, missing economists' expectations in a Reuters poll that it would remain at the March level of 1.3%.  

The weak reading follows disappointing GDP, output, export and sentiment figures.

These suggest that euro zone economic growth has peaked after a five-year run and will at best slow to a more moderate level, below optimistic forecasts at the start of the year. 

This comes at a sensitive time for the ECB as policymakers are debating whether to end a €2.55 trillion bond buying scheme this year, satisfied that healthy growth will eventually raise inflation back to its target of almost 2%. 

Introduced more than three years ago to boost flagging growth and inflation, the ECB's bond purchases helped to revive the economy with a flood of cheap cash. 

The programme is due to run out at the end of September and policymakers need to decide over the summer whether to shut it down after several extensions. 

But inflation has failed to rise for years according to expectations and in April it also missed the ECB's prediction of a rate "around" 1.5% for the rest of the year. 

Perhaps more worryingly for the ECB, all measures of closely-watched underlying inflation fell, indicating that pressures remain weak, despite robust employment growth and a healthy wage deal in Germany, the bloc's biggest economy. 

Inflation excluding volatile food and energy prices, the ECB's preferred measure, slowed to 1.1% from 1.3%. 

The rate excluding energy, food, alcohol and tobacco, an even more narrow measure often looked at by market analysts, eased to 0.7% from 1%. 

ECB chief economist Peter Praet said the slowdown had come sooner than expected and factors holding back growth may persist in the near term, but he played down the data. 

"We cannot yet declare 'mission accomplished' on the inflation front, but we have made substantial progress on the path towards a sustained adjustment in inflation," he said in Paris.