The pope is responsible for the Vatican's growing hostility towards Turkey joining the EU, previously secret cables sent from the US embassy to the Holy See in Rome claim.
In 2004 Cardinal Ratzinger, the future pope, spoke out against letting a Muslim state join, although at the time the Vatican was formally neutral on the question.
The Vatican's acting foreign minister, Monsignor Pietro Parolin, responded by telling US diplomats that Ratzinger's comments were his own rather than the official Vatican position.
The cable released by WikiLeaks shows that Ratzinger was the leading voice behind the Holy See's unsuccessful drive to secure a reference to Europe's "Christian roots" in the EU constitution. The US diplomat noted that Ratzinger "clearly understands that allowing a Muslim country into the EU would further weaken his case for Europe's Christian foundations".
The cables reveal the American government lobbying within Rome and Ankara for Turkish EU membership.