France has deployed 7,000 soldiers following a stabbing at a school which killed one person and wounded three others.
The man killed was a French language teacher, while three others seriously wounded and are now in hospital.
Following the incident, French prime minister Elisabeth Borne raised the level after a security meeting with President Emmanuel Macron.
Amid an increased terror level, the Louvre museum in Paris was evacuated following a written threat.
The museum said the move was linked to the government’s decision to put France on high alert after the fatal school stabbing in Arras by a suspected extremist.
The Louvre communication service said no one has been hurt and no incident has been reported.
Alarms rang out through the vast museum in central Paris overlooking the Seine River when the evacuation was announced, and in the underground shopping centre beneath its signature pyramid.
Police cordoned off the monument from all sides, and the underground access, as tourists and other visitors streamed out.
Videos posted online showed people leaving, some hurriedly and some stopping to take photos, others apparently confused about what was happening.