It’s unclear what motivated the incident, though French prosecutors have opened a terrorism investigation into it. A French Interior Ministry spokesperson said it was “too early” to identify a motive in the attack, according to Reuters, but said on BFM TV, a French television network, that the police officers were deliberately targeted.

U.S. President Donald Trump, however, suggested terrorism as motivation. “It’s a terrible thing…it looks like another terrorist attack. What can you say. It never ends,” he said at a press conference on Thursday.

At least two attackers fired the shots, according to Reuters. One got out of a car at the scene and began firing a machine gun, officials said. One shooter was killed, officials said, later adding that the shooter was known to security services. Police began searching the home of the dead attacker, Reuters reports.