An attacker with an automatic weapon opened fire on police on Paris’ iconic Champs-Elysees Thursday night, killing one officer and seriously wounding two others before police shot and killed him.

Paris police spokeswoman Johanna Primevert told The Associated Press that the attacker targeted officers guarding the area near the Franklin Roosevelt subway station at the center of the shopping avenue popular with tourists. She said he appeared to be acting alone.

Police and soldiers sealed off the area, ordering tourists back into their hotels and blocking people from approaching the scene.

The Paris prosecutor’s office said counterterrorism investigators are involved in the probe. Two police officials, speaking on condition of anonymity to discuss the ongoing investigation, said the attacker had been flagged as an extremist. They had no other details about him.

The attack came three days before the first round of balloting in France’s tense presidential election. Security is high preceding the vote after police said they arrested two men Tuesday in what they described as a thwarted terror attack.