Germany's president is widely expected to label the slaughter of Armenians by Ottoman Turks a century ago as genocide, underlining a shift in his country's stance after it previously avoided the term.

President Joachim Gauck will speak Thursday at a nondenominational service commemorating what the churches organizing it call genocide — a day before Germany's Parliament debates a motion that describes the killings as "exemplary" for the 20th century's history of expulsions and genocide.

The government has backed that formulation and said it was in contact with Gauck's office on his speech.

Turkey has lobbied fiercely to prevent countries from recognizing the massacres as genocide. It recalled its ambassador to the Vatican after Pope Francis used the term and its ambassador to Austria after lawmakers in Vienna did so.