A bomb attack on a World War I remembrance ceremony at a cemetery in the Saudi Arabian city of Jeddah wounded several people on Wednesday, France said, urging its citizens living in the conservative kingdom to exercise maximum vigilance.

France’s foreign ministry said the attack had taken place at a ceremony in the Red Sea port city involving foreign embassies, and that an explosive device had been used. A Greek official said four people had been wounded.

“There was some sort of a blast at the non-Muslim cemetery in Jeddah. There are four slightly injured, among them one Greek,” the Greek official said, declining to named.

“The embassies that were involved in the commemoration ceremony condemn this cowardly attack, which is completely unjustified,” a French foreign ministry statement said. “They call on the Saudi authorities to shed as much light as they can on this attack, and to identify and hunt down the perpetrators.”

The French consulate in Jeddah, in a statement seen by Reuters, urged its nationals in Saudi Arabia to exercise “maximum vigilance” following the attack. “In particular, exercise discretion, stay away from all gatherings and be cautious when moving around,” said the statement. It said only two people had been injured.

A source with knowledge of the matter said the attack happened early on Wednesday when several EU diplomatic delegations were present at a Remembrance Day event organised by the French embassy.