French President Emmanuel Macron has said that a knife attack that killed one person and injured three others in eastern France on Saturday was an act of Islamist terrorism. This comes after the French anti-terrorism prosecutor’s office confirmed that it was investigating the case.

As he began his attack, the 37-year-old was heard shouting, “Allahu akbar,” according to France’s antiterrorism police. The Arabic phrase, meaning “God is great,” is an everyday expression used in religious and nonreligious settings alike, but has also become a war cry in some terrorist attacks by Islamic fundamentalists.