A valuable diamond necklace by Parisian luxury jewelry house Van Cleef & Arpels was stolen from the Museum of Applied Arts in Vienna during opening hours.

Austrian police said two unidentified men dressed in dark clothing smashed a glass display case, stole the necklace and fled the scene, according to the DPA news agency. No one was injured.

The museum confirmed that the necklace had been stolen from an exhibition featuring more than 300 objects but provided no details about the investigation. According to the museum’s website, the royal jewel contains 673 diamonds weighing more than 200 carats.

The historic necklace once belonged to Queen Nazli of Egypt, who wore it at her daughter’s wedding in 1939. According to Sotheby’s, the unique piece sold at auction in New York in 2015 for approximately $4.3m.

Police have released images of the suspects and are conducting an intensive search for them.

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