The Louvre Museum in Paris is evacuating all visitors and staff and closing early Saturday because it received a written threat.
It said the move was linked to the government's decision to put France on high alert after a fatal school stabbing by a suspected extremist.
The Louvre communication service said no one has been hurt and no incident has been reported.
Paris police said verifications in the museum are underway. Police officers cordoned off the area as tourists and other visitors streamed out of the museum.
The French government raised the threat alert level and is deploying 7,000 troops to increase security after Friday's school attack.
The government is also concerned about fallout in France from the war between Israel and Hamas.
The Louvre, home to masterpieces such as the Mona Lisa, welcomes between 30,000 and 40,000 visitors per day.
