A soldier patrols at the Eiffel Tower, Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
Police officers patrol on the Trocadero square Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
A soldier patrols at the Eiffel Tower, Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
Police patrol nearby the Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
Police officers patrol on the Trocadero square Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
Soldiers patrol in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
Soldiers patrol in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
A soldier patrols at the Eiffel Tower, Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
A Serbian special police officer patrols at a shopping mall in Belgrade, Serbia, Monday, March 25, 2024. Serbian government increased its security alert posture after the deadly attack at a Russian concert hall. (AP Photo/Darko Vojinovic)
Serbian special police officers patrol at a shopping mall in Belgrade, Serbia, Monday, March 25, 2024. Serbian government increased its security alert posture after the deadly attack at a Russian concert hall. (AP Photo/Darko Vojinovic)
Soldiers patrol in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
A soldier patrols in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
Tourist stand by a sign alerting on France's highest security level at the Louvre museum, Monday, March 25, 2024 in Paris. France's government increased its security alert posture to the highest level Sunday March 24, 2024 after the deadly attack at a Russian concert hall and the Islamic State's claim of responsibility. (AP Photo/Michel Euler)
Police patrol in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
Police patrol in front of Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)
Police patrol near by the Milan gothic cathedral in Milan, Monday, March 25, 2024. Italy followed France Monday in stepping up its security stance following the attack on a suburban Moscow concert hall and the claim of responsibility by an affiliate of the Islamic State group. (AP Photo/Luca Bruno)