Thieves broke into the René Lalique museum in the town of Wingen-sur-Moder in northeastern France early Sunday and stole jewellery worth about €4 million, an investigation source said.

Authorities said the suspects entered the museum around 5:30 a.m. after forcing access and then went directly to the jewellery room. Around twenty pieces of jewellery were taken, with officials estimating the value could be close to four million euros as damage and missing items were assessed.

The theft involved the smashing or forcing open of display areas, and the museum’s alarm was reported to have sounded. The museum was temporarily closed as investigators gathered evidence and assessed the extent of the break-in.

Police are investigating how the thieves carried out the attack and whether they had prior information about the jewellery displayed.