PARIS (AP) — Paris police say a security operation is underway in the Champs-Elysees shopping district and are urging people to avoid the area.

The police department tweeted the warning Monday without providing further details. The high-end neighborhood is popular with tourists.

The reason for the operation remains unclear.

A subway station in the area is closed.

An attacker defending the Islamic State group shot and killed a police officer on the Champs-Elysees in April, days before a presidential election, prompting an extensive security operation. France is under a state of emergency after a string of deadly Islamic extremist attacks.