A French consulate worker faced charges on Monday of using an official car to smuggle dozens of guns from the Gaza Strip to the occupied West Bank, in a case Israeli authorities called "very severe".
Israeli officials noted the worker from France's Jerusalem consulate acted on his own without his superiors' knowledge and that diplomatic relations between the two countries were not affected.
But the delicate case comes ahead of a planned visit to Israel and the Palestinian territories next week by French Foreign Minister Jean-Yves Le Drian, and French diplomats are sure to face questions over it.
The arrested French citizen and several Palestinian suspects are accused of belonging to a gun-running network that sold the weapons to arms dealers, Israel's Shin Bet domestic security agency said.
It alleged that Romain Franck, 23, had taken advantage of reduced security checks for consular vehicles to transport the weapons out of the Palestinian enclave.
Shin Bet said he was motivated by money. "The consulate employee smuggled the arms on a number of occasions in recent months while using the French consulate's consular car, which underwent a more lax security inspection at the border crossing, as is the case with this type of car," it said.
"The consulate employee transferred arms on five occasions, during which he transferred some 70 pistols and two automatic rifles."
Nine suspects were arrested and six faced charges in court on Monday, including Mr Franck.
A resident of East Jerusalem who works as a security guard at the French consulate was among them, Shin Bet said.
The French consulate employee allegedly received the guns from a Palestinian in Gaza who worked at the French Cultural Centre in the Strip.
He smuggled them into the West Bank to another person who sold them on to arms dealers, it said.
Gaza, run by Hamas, has been under an Israeli blockade for more than a decade but weapons have been smuggled in through tunnels from Egypt's Sinai Peninsula.
News of the February 15 arrest emerged on Sunday, but the details were still unclear.
A spokesman for France's embassy in Israel said Sunday "we take this case very seriously and are in close contact with the Israeli authorities".
Mr Franck "has benefited and continues to enjoy the consular protection" provided to French nationals, he said.
Shin Bet called the incident "very severe", saying that "the immunity and privileges given to foreign representatives were cynically abused to smuggle dozens of weapons that could be used for terror attacks against Israeli civilians and security forces".
"The investigation was conducted in co-operation with the Israeli foreign ministry while constantly updating the French authorities," it said.
An Israeli official said on condition of anonymity that while authorities were taking the case "very seriously," diplomatic relations were not affected.
"Relations with France are excellent and won't be affected by this affair," the official said. "We thank the French authorities for their co-operation."
Those entering and exiting the Gaza Strip through the Erez crossing with Israel undergo strict security checks by Israeli authorities, but these measures are eased for diplomatic visitors.
The Palestinian enclave, home to two million people, is sealed off from Israel by a wall.
Israel and Palestinian militants in Gaza have fought three wars since 2008.
Yoav "Poli" Mordechai, the Israeli defence ministry official who oversees civilian affairs in the Palestinian territories, said the case "sharpens the need for a severe and strict policy of granting permits" related to the Gaza Strip.
Israeli authorities carry out regular operations to seize weapons in the West Bank, which has been under Israeli occupation since 1967.