Brussels called for "complete vigilance" Monday to stop the spread of a strain of bacteria killing olive trees in southern Italy, the European Union's second biggest producer of olive oil.

EU Health Commissioner Vytenis Andriukaitis said he would travel to Italy soon to study the effectiveness of measures to halt the epidemic of xylella fastidiosa, which emerged in 2013 and also threatens citrus fruit and vineyards.

Italy has marked off an emergency area of 241,000 hectares (593,000 acres) in the southern Puglia region that is affected by the disease, which causes the trees to wither away and for which there is so far no remedy.

Studies showed at least 10 percent of some 11 million olive trees in the worst-affected Lecce area of Puglia had the bacteria, the commissioner told the European Parliament's agriculture committee.

He said the EU was "following the situation very closely" and encouraging a cautious approach by having blighted trees uprooted.

The disease threatens to have a major economic impact as Italy is second only to Spain as the biggest producer of olive oil in the 28-nation bloc.

But EU officials said Italy had worsened the situation by dragging its feet under pressure from growers.

A special EU committee is due to consider new approaches during its next meeting on March 26-27 as France, Spain and Portugal call for a toughening of prevention measures.

But resistance is growing in Italy against the destruction of age-old olive groves.

In a letter to Andriukaitis, the Italian environmental association Peacelink pointed to scientific studies blaming a type of fungi rather than the xylella fastidiosa bacteria for blighting the olive trees.

"The European Commission risks condemning to death the whole Puglia ecosystem on the basis of results of tests that have not even ascertained the pathogenicity of xylella in those trees," it warned.