The latest blow to European unity - the failure to agree on a 2006-2013 budget - came quick on the heels of founding members France and Holland's rejection of the EU constitution.
The failure to agree on the constitution revealed deep anxieties in both countries over future Turkish membership.
The constitution's author, former president of France Valery Giscard d'Estang, went so far as to blame the Turkish membership issue for the double rejection of the constitution.
At the same time, the German opposition Christian Democrat Union (CDU) - who are on course to win September's early elections - have said they are opposed to Turkey's membership.
Recent debate on enlargement has also caused anxiety in other prospective EU member countries Romania and Bulgaria -which are set to join in 2007 - and in Croatia.
A Christian club?
However, "Turkish membership has always been different from the other candidates," Sedat Laciner, director of the Ankara-based think-tank, the International Strategic Research Organisation, told Aljazeera.net.
"This is because the other European countries don't really consider Turkey a European country, as Turkey is the only Muslim candidate."
Turkey eyes the referendum's
rejection with apprehension
Such a view has often led in the past to allegations from Ankara that the EU is a Christian club. Now, some argue, Europe's basic prejudices are coming out as the union faces a crisis.
But this is a view denied by European leaders, who decided last December to give Turkey a 3 October 2005 date to begin accession talks - more than 40 years after Turkey first applied to join.
"The EU has to stick to its existing commitments," European Commission spokesperson Krisztina Nagy told Aljazeera.net on Friday.
"The talks will begin on October 3 provided Turkey fulfils the necessary conditions."
However, these conditions are already proving difficult for Ankara to meet.
Turkey undertook last December to extend the Ankara Agreement - a deal between the country and the EU over customs and trade - to include all the EU's latest members. Since May 2004, the new EU countries have included the Republic of Cyprus, which Turkey does not recognise and with which it has long had hostile relations.
Many Turks resent the idea of having to include the Greek Cypriot-dominated Republic in any official relationship -preferring instead to champion the cause of the internationally unrecognised Turkish Republic of Northern Cyprus, the isolated breakaway state in the north of the island.
Turkey has recognised Cyprus as
part of a customs agreement
"The EU has to take some steps on Cyprus too," says Zeynep Ersahin, research fellow at the Bosphorus University-TUSIAD Foreign Policy Forum.
She points to the fact that Brussels promised to assist the Turkish Cypriots, who voted last year in favour of the last United Nations plan to reunify the island, while the Greek Cypriots voted against it.
"After the referendum, however, the EU did not take any action," she says.
Revamped penal code
At the same time, Turkey also agreed as a precondition for accession talks that it would enforce six pieces of legislation that would bring the country more in line with EU norms. These included a revamped penal code, which went through parliament in Ankara on 1 June.
"The EU is always emphasising that legislation adopted has to be implemented," says Nagy. This, too, is a major sticking point, as it requires potentially open-ended-on-the-ground evaluation.
Recent heightened violence in Turkey's southeast between the army and Kurdish separatists has also called this implementation into question.
Recent violence in southeast
Turkey worries the EU
Dutch ambassador to Ankara Sjoerd Gosses said earlier this week that the EU stood for "the integration, not ... disintegration" of its future members, backing calls from the European Commission for Turkey to find a civil alternative to its military campaign against the separatists.
The EU argues that the southeast is effectively run by the Turkish military, rather than civilian authorities.
Then there is the long-running Armenian question. On 16 June, the German parliament passed a resolution acknowledging the massacres of Armenian citizens of the Ottoman Empire back in 1915 by Ottoman troops and irregulars.
Stopping short of labelling these events 'genocide', the Germans called on Turkey to acknowledge the massacres -something it has always been wary of doing.
While the EU itself has made no such demand on Turkey, it has called for a normalisation of Turkey's relations with neighbouring Armenia, a process which inevitably involves the events of 1915.
"This was almost 100 years ago," says Laciner. "And the EU makes no mention of the current Armenian occupation of Azeri territory."
Relations with Armenia have
been a thorny issue for Turkey
In the conflict over the enclave of Nagorno Karabakh in the early 1990s, Armenian forces took a swathe of land from Turkish ally Azerbaijan, linking the enclave to their border.
"People in Turkey see this as an example of Christian solidarity. Just focusing on the events of 100 years ago shows the EU is not sincere," Laciner told Aljazeera.net.
However, despite this range of disputes, some Turks remain optimistic about their EU chances.
"I don't think Turkey's EU membership can be looked at from the perspective of the recent referendums on the EU constitution," says Ersahin, pointing to the recent Eurobarometre poll which found that only 6% of French respondents voted against the constitution because of Turkey.
In Holland, the figure was even lower, at only 3%. Most voted 'no' because of concerns over unemployment and the local economy.
"The EU has to deal with its own economic and social problems first and Turkey later," Ersahin says. "Accession is a process, which can go up or down.
"Turkey has made great strides on many issues, and while there will be many discussions on the shape of the EU in the future, the EU is the most successful integration process of the century. It may take 10 to 15 years, but Turkey will become an EU member."
"Yes, there are many problems here in Turkey," acknowledges Laciner. "But the EU has already said Turkey is a candidate and that these problems can be solved. Up to now, Turkey has done what the EU wanted in terms of reforms and the Europeans have acknowledged this."
The pressure, however, is likely to be growing not just on Turkey to fulfil its commitments, but on the EU to carry through with its obligations.
"The EU is a community of commitments," says Nagy, "and those that have been taken have to be met."