Two thieves stole a €70,000 ($93,000) diamond ring from a Cannes jewellery store , pocketing the gem while a saleslady had her back turned, a police source said.
Police in the French Riviera resort town - which has been hit by a series of spectacular jewellery heists this year - said the men had eastern European accents.
They pilfered the ring from a jewellery store near the luxury Gray d'Albion hotel.
Police have opened an investigation and said they will examine security videos for evidence.
On July 28, an armed man pulled off a brazen heist in broad daylight at the luxury Carlton Hotel in the town, in one of the world's biggest jewellery heists.
Brandishing a semi-automatic pistol, his head covered with a cloth, the robber stole jewels that were part of an exhibition by a group owned by Israeli billionaire Lev Leviev.
French authorities said he escaped with all kinds of jewellery, including rings, pendants, and diamond-encrusted earrings, worth an estimated €103 million.
Cannes has fallen prey to other jewel thefts several times recently, and during this year's film festival in May.
The festival, which attracts a glittering array of celebrities thieves stole jewellery worth $1.4 million due to be loaned to movie stars.
Yet another theft during the festival saw robbers make off with a diamond necklace with an estimated value of $1.9 million.
At least two apartments rented by film executives were also burgled during the 2013 festival, with thieves taking cash, jewellery and other personal items.