The Louvre museum and the Château de Versailles, in Paris, France, were evacuated and closed on Saturday afternoon after staff at the museum received a written security threat.A statement posted on the museum’s website said: “For safety reasons, the museum is closed.”The Louvre, the home of Leonardo da Vinci’s Mona Lisa and the most visited art gallery in the world, urgently ejected all visitors on its premises amid a heavy police presence and alarms that were audible across the centre of Paris. Fifteen thousand visitors were evacuated, with a comparable number also being told to leave the château and park in Versailles, the historic palace on the outskirts of the city.“The Louvre received a written message stating that there was a risk to the museum and its visitors,” a museum spokesperson told the Agence France-Presse news agency. “We have decided to evacuate and close it for the day, while we carry out the necessary checks.”Police cordoned off the museum before conducting a full search of its galleries. The palace of Versailles, as well as its huge gardens, were also searched. No incident was reported and both sites reopened for visitors on Sunday. France’s home minister Gerald Darmanin later said there was “no real threat”.One visitor told the French newspaper Le Parisien: “The Louvre did not explain why we needed to evacuate, which was a good thing because the exiting crowd was blocked at the main entrance”.France has been placed under the maximum security alert in the wake of the Hamas attack in Israel and the resulting Israeli offensive against Gaza, and in the days after a suspected terrorist attacks in the north of the country.On Friday, a teacher was stabbed to death in a high school in the northern French town of Arras, reportedly by a Russian-born Chechen, aged 20. Three school staff were also injured, with two in a critical condition. The attack came almost three years to the day after teacher Samuel Paty was killed also by an Islamist terrorist in a town just west of Paris.The French government have deployed seven thousand soldiers to assist police as a result of the security alert. France has not been placed under such a high security level since Operation Sentinel, which was set up after the attacks in Paris in November 2015 by the so-called Islamic State terrorist group.In a nationally televised address on Thursday evening, President Emmanuel Macron said police and military protection was being stepped up at 582 religious and cultural sites across France. The government has also banned all pro-Palestinian demonstrations.In Paris, the Arab World Institute decided to postpone all conferences and debates planned for their scheduled Palestinian Season. A concert was also cancelled as the musicians due to perform are unable to leave Gaza, and the Institute considered that other musical events had to be delayed “out of respect of the victims,” according to an official source.