The letter was sent on Dec. 12 to 23 EU leaders, except Greek and Greek Cypriot leaders.
Mesrob Mutafian reminded EU leaders the obligations of the union and asked them to fulfill their promises.
The Armenian patriarch said Mustafa Kemal urged Turkey in the 1920s to turn to the West, adding: "It is of utmost significance that the EU should not force Turkey to fulfill multifaceted conditions and derail negotiations, while ignoring its obligations."
Mutafian said as the leader of the Armenian Orthodox community he wanted to convey his opinions and concerns ahead of the council meeting started the previous day, and indicated that EU leaders' decision regarding Turkey would have impacts in a wide context.
The current impasse over Turkey-EU relations would put Turkey's accession process to the union in a risky position, the Patriarch said, adding: "This critical period should be handled with responsibility."