The comment is a reference to French president Nicolas Sarkozy's intention to make the EU have a debate on its final borders, with December slated as the date.

Mr Sarkozy is opposed to Turkish EU membership, something he has repeated on several occasions, and believes that a debate on the issue is "unavoidable."

So far the French idea has been met with little enthusiasm from other member states, with several concerned that forcing the EU's hand on this issue will only expose its differences.

The Portuguese EU presidency, in place until the end of the year, has on several occasions indicated it is not in favour of the debate.

"The accession process is an anchor for democracy and secularism," said Mr Rehn. "Both currents - the secular as well as the post-Islamic - are moderate when the country's progress is linked to EU accession."

If a "member state or a group wants to put the taken path into question, then it has to take responsibility for the consequences."

The unusually strong rebuke from the commission is a sign of its concern over the direction Turkey, a moderate mainly Muslim-populated land, could eventually take if it is perceived as unwanted by the 27-member union.

According to Mr Rehn, half-hearted statements by EU politicians are used by parties who see the bloc as an enemy to strengthen their position.

With the uncertain voices coming out of the EU, Turkey's parliamentary elections on 22 July have taken on great significance, with Brussels worried the bloc's ambivalent stance could boost nationalist right wing forces to do better at the polls.

A commentator in Turkish newspaper TZ called it "the most critical elections in the history of Turkish democracy."

On top of wanting member states to make good on its promises to conduct EU membership negotiations with Turkey – these were opened in autumn 2005 – there is also the pragmatic element to the whole debate.

Turkey is a transit land for up to 15 percent of the oil and gas needs for Europe, said the commissioner.