PARIS — British insurers announced on Tuesday they are offering a reward of one million euros, or $1.33 million, for information leading to the recovery of millions of dollars of diamonds stolen in France’s biggest jewel heist on record.


On July 28, a lone armed robber made off with a case of gems valued at $136 million at retail, which were destined for a temporary exhibit by jeweler Leviev at the Carlton hotel in Cannes.


“A reward of up to 1 million euros pro rata is offered to the first person who provides information which leads to recovery of the goods,” said a statement issued by S.W. Associates, an independent French company of chartered loss adjusters, risk managers and surveyors, on behalf of the Lloyd’s of London insurance market.


The announcement, which features a phone number and an e-mail address, will be published on Wednesday in French newspapers Nice-Matin and Le Parisien, in addition to the International Herald Tribune. It is accompanied by photographs of two rings, a brooch and a pendant that were among the stolen items.


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French Interior Minister Manuel Valls headed to Cannes on Tuesday to review security arrangements at the French Riviera resort, which has been the target of a series of high-profile holdups by jewelry thieves in the last few months.


In a separate incident last week, two armed robbers made off with a stash of luxury watches from the Kronometry store, located on the Boulevard de la Croisette opposite the Palais des Festivals.


Jewel thieves struck twice during the Cannes film festival in May, making off with $1 million worth of gems from the hotel room of an employee of Swiss jewelry and watch firm Chopard, and stealing a De Grisogono necklace valued at 2 million euros, or $2.6 million, during a star-studded party at Cap d’Antibes.


Adolphe Colrat, prefect of the Alpes-Maritimes department, last week dispatched police reinforcements to the town and called a meeting on Aug. 8 to discuss the creation of a Comité Croisette that would group together leading retailers and hoteliers, along the lines of the Comité Vendôme created in Paris in 1936.


The idea is to gather all the luxury players exposed to risk and to give them a joint platform to communicate with government officials, in particular the national police, he said.