The motorcade of a Saudi prince was attacked Sunday evening in a suburb of Paris, with up to eight armed men stopping the convoy and taking a suitcase containing more than $335,000 in cash and sensitive documents.

The attackers kidnapped a driver, a bodyguard and another employee but later released them. No one was reported hurt in the attack, which occurred as the motorcade was heading toward an airport in the northeastern suburb of Le Bourget.

French media quoted officials describing the attack, which occurred between 9 and 10 p.m. local time, as “well-informed,” “unusual” and “rare.”

Investigators have opened an investigation, but so far no suspects have been apprehended. Two cars that had been used by the thieves were later found burned out.

An unnamed investigator told the French newspaper Le Monde that the nature of the case would change if it is determined that the thieves had specifically targeted the sensitive diplomatic documents. “In that case we would no longer deal with banditry, but instead with something more complex,” the source said, according to the newspaper.

The unnamed official went on to say that an early assessment of the attack had concluded that the thieves must have been aware of the suitcase’s location in the motorcade, which included approximately 10 vehicles. So far, Saudi Arabia’s embassy in Paris has not commented on the incident.

The French capital has recently seen a series of thefts of luxury items, such as jewelry, as well as robberies targeting foreigners. In an incident last year, thieves stole passports, plane tickets and a substantial amount of cash from Chinese tourists.

By attacking a diplomatic convoy, however, the thieves have caught the attention of the French Foreign Ministry, which is widely known as Quai d’Orsay. The Guardian cited ministry spokesman Romain Nadal as calling Monday’s attack unacceptable. Under international law, France has to ensure the safety of foreign diplomats.

A particularly harsh violation of that rule was the 1979-1980 Iranian hostage crisis, in which the government in Tehran refused to help American diplomats held in the U.S. Embassy. Diplomatic relations were canceled in response, and the repercussions of that incident are still felt today, reflecting the severity of an attack on diplomatic property.