ANKARA (Reuters) - The administrators of a prestigious Istanbul high school have warned teachers over Christian and Christmas-related content in German language classes, the school said on Monday, setting the stage for another diplomatic row between Ankara and Berlin.

Entrance to the German high school in Istanbul March 17, 2016, when it was closed due to an "unconfirmed warning". REUTERS/Murad Sezer

Relations between Germany and Turkey, a candidate to join the European Union, have been strained following a failed coup in July as Turkish authorities have detained, suspended or arrested more than 100,000 people, leading to widespread concern in Europe about the rule of law in Turkey.

The Istanbul Lisesi, a state-run high school that offers a curriculum in both German and Turkish, said in a statement that administrators had met the head of the German department over concerns that teachers were devoting too much time teaching about Christmas and Christianity.

“When we received information that German teachers were teaching increasingly more texts on Christmas and Christianity in a manner that is outside the curriculum ... our administration arranged a meeting with the German department and requested information,” the school said.

“It is out of the question to have any approach inside of the school that limits the most natural right of freedom of belief of German and Turkish teachers, students and personnel.”

A largely Muslim country, Turkey is constitutionally secular, though President Tayyip Erdogan and the ruling AK Party he founded have their roots in political Islam and have tried to restore the role of religion in public life.

German media had widely reported that the school had banned its annual Christmas concert and some German politicians urged the government to summon the Turkish ambassador to complain.

However, a spokesman for the German foreign ministry said Berlin was hopeful the issue would be resolved after talks between German and Turkish staff at the school. He said the school had never imposed a ban on celebrating Christmas.

The school said in its statement that the concert had been cancelled by the German teachers themselves for unknown reasons.

However, one senior AKP lawmaker equated the teachers with “missionaries” and said Germany was attempting to subject Turkish children to propaganda.

“Being a missionary is not allowed in public school,” Mustafa Sentop said on Twitter. “The religious/political propaganda of the German state to this nation’s children is not allowed in public schools,” he said.