The European Commission, the EU's executive arm, has approved a report judging that 10 countries would be ready to join the Western club by 2004, but proposed no time frame for launching membership negotiations with Turkey.
Turkey has already expressed its anger at the report, and late on Wednesday the US State Department weighed in, saying it saw Turkey as a vital ally in Europe.
Turkey has a close military relationship with the US, hosting part of the US air force at the Incirlik air base, and its co-operation would be vital in any possible forthcoming US attack on Iraq.
Turkish disappointment
The EU report said Turkey had failed to meet the criteria necessary to join the current round of EU expansion, noting in particular its human rights record.
Candidates shortlist
Cyprus
Czech Republic
Estonia
Hungary
Latvia
Lithuania
Malta
Poland
Slovakia
Slovenia
The Turkish Government said it hoped it would still be included following an EU summit in Copenhagen in December, and warned it might revoke agreements with the EU if moves towards membership are delayed.
At the US State Department, spokesman Richard Boucher said Washington had "long believed that Turkey's future is in Europe".
"It's in the strategic interest of the United States and the European Union, Turkey and the European Union, that Turkey and the European Union build the closest possible relationship," he said.
Trade threat
Turkey expressed anger that the EU had not recognised recent efforts towards meeting criteria for accession talks.
Click here to see a map of EU applicants
The EU said Turkey had not reached minimum economic and political standards for membership, and needed to improve its record on human rights.
Turkey has made extensive reforms to its legal system over the summer, abolishing the death penalty and lifting restrictions on the use of the Kurdish language.
Turkish Foreign Minister Sukru Sina Gurel told the BBC Ankara might reconsider a six-year-old trade pact with the EU.
"If disappointments in the field of candidacy or accession process of Turkey to the European Union is witnessed in the near future, of course the customs union arrangement will have to be reviewed," he said.
Mr Gurel said Turkey hoped a "political decision" at the EU summit in Copenhagen would be made in Turkey's favour.
"
I have high hopes for enlargement
"
John Adlington, UK
Related to this story:
EU reaches landmark expansion deal
(09 Oct 02 | Europe)
The EU's uneven new contingent
(09 Oct 02 | Europe)
Q&A: European enlargement
(09 Oct 02 | Europe)
At-a-glance: EU enlargement
(08 Oct 02 | Business)
Turkey's EU membership argument
(09 Oct 02 | Europe)