The world-renowned Louvre museum in Paris was shut on Sunday after several pieces of invaluable jewelry were stolen in a brazen robbery.

Speaking to France Inter radio station on Sunday, Interior Minister Laurent Nunez said that several individuals entered the Louvre that morning during what he called a “major robbery” that lasted minutes. According to the former Paris police chief, it was “clearly a team that had done their homework” as the windows were cut with a power tool.

“Jewelry that has historical and priceless value” had been taken, Nunez said. “But I can’t tell you any more at this time.”

“We are working hard at the moment to find the perpetrators,” he added, while confirming that no one was injured.

Culture Minister Rachida Dati later told TF1 that the gang broke into the Galerie d’Apollon — a sumptuous room on the first floor of the Petite Galerie that has housed the French crown jewels since 1887 — and that a piece of jewelry was recovered during the escape. Several pieces of jewelry belonging to Napoleon and the Empress Eugenie had been stolen, according to French newspaper Le Parisien.

A global symbol of French culture, the Louvre is one of the most heavily guarded places in the capital. Despite its security, the museum has at times been breached, most famously in 1911 when Leonardo Da Vinci’s Mona Lisa was stolen. Other attempts targeted works including Eugene Delacroix’s Liberty Leading the People, as well as Gustave Courbet’s The Wave.

Following the heist, the Paris public prosecutor’s office announced an investigation into “organized theft and criminal conspiracy to commit a crime.”

According to the Minister of the Interior, three or four thieves arrived near the museum on powerful TMax scooters on Sunday morning around 9:30 a.m. The perpetrators fled the scene and are being sought, Nunez said.

The incident is likely to increase scrutiny on the vulnerability of France’s museums and cultural institutions to organized crime. Just last month, thieves broke into Paris’s Natural History Museum, stealing rare gold nuggets worth an estimated €600,000 ($702,600) as bullion prices surged, according to French newspaper reports.

Earlier this year, French President Emmanuel Macron unveiled an ambitious 10-year “Renaissance” project to renovate the Louvre, which included plans to secure the museum’s premises.

“The vulnerability of museums is a long-standing issue,” Dati said. “These museums must be adapted to new forms of crime.”