Turk told the European Parliament accession negotiations with Turkey must continue. He called on fellow EU countries to show pragmatism in admitting new countries - although he said any prospective member must first fulfill all technical criteria.
No country "can be precluded from membership only for reasons of political inconvenience or cultural prejudice," said Turk, whose country holds the rotating EU presidency until June 30.
Turkey's membership should continue and EU should not deprive Turkey of the full membership target it had granted, otherwise the union's prestige would be overshadowed, he added.
Turkey's EU campaign, which is expected to last many years, has already been damaged by political repercussions such as French and German misgivings and the Cyprus issue. France takes over from Slovenia as the EU president on July 1.
But Turk said the EU needs Turkey, and a failure to engage Ankara would damage the EU's credibility. "The feeling of exclusion breeds resentment, and resentment breeds instability. We must think about further expansion in the light of the EUs ambition to be a leading global player."
The EU had started negotiations with Turkey in 2005 but last year suspended negotiations on eight policy chapters due to Ankara's refusion to open its ports to Greek Cypriot vessels.