France is boosting security at Jewish religious sites after blank bullets were fired on a synagogue west of Paris, and amid renewed concerns about anti-Semitism around the country.

French President Francois Hollande met Sunday with leaders of the country's Jewish community, and pledged to fight extremism and anti-Semitism "with the greatest firmness."

He said that authorities "in the coming days, in the coming hours" will increase security at Jewish religious sites so they won't be subject to the kind of attack that targeted a synagogue in the Paris suburb of Argenteuil on Saturday night.

A representative of the synagogue says the building was targeted with about eight blank bullets and services were cancelled. The representative, who spoke on condition of anonymity because a police investigation is under way, said no one was hurt in the incident.

The attack on the synagogue came hours after police carried out raids across France against suspected Islamist cells. According to preliminary witness statements, the shots came from a car which slowed down as it approached the synagogue, before accelerating and fleeing the scene.

"A person… heard a bang and saw flashes. They fired blanks; there were no impact signs from the bullets," a witness told police.

Board of Jewish Communities in Val-d'Oise Chairman Moshe Cohen-Sabban told Le Parisien: "This was an act that was more against the Jewish community. This is very worrying."

Meanwhile, the police raids earlier in the day were based on DNA taken from a grenade that exploded last month at a kosher grocery store, which led them to a suspected jihadist cell of young Frenchmen recently converted to Islam.

The man whose DNA was identified, named by police as Jeremy Sydney, was killed by police after he opened fire on them, wounding three officers in the eastern city of Strasbourg. Officials said he had been under surveillance since last spring — around the time a French Islamic terrorist went on a shooting rampage against a Jewish school and French soldiers, killing seven people.

The police unit was fired on after entering a fourth-floor apartment at about 6 a.m. (0400 GMT) in the Esplanade district of Strasbourg and an officer was wounded by shots that hit his bulletproof vest and helmet.

"During an anti-terrorist police operation in Strasbourg ... gunfire was exchanged between police and the suspect. The latter was killed," Strasbourg prosecutor Patrick Poirret said in a statement.

"The group was met with a .357 Magnum [revolver]," said Norbert Georgel, secretary for the region's police union, who said the wounded officer's life was not in danger.

Neighbors told Reuters that a couple had lived in the apartment with their two children for the past four to six months. The man was bearded and the woman wore the Muslim full-face veil, they said.

Reuters could not immediately confirm whether that man was the suspect shot by police.

The French Interior Ministry declined comment.

Eleven other suspects were arrested across the country Saturday, according to the Sipa news agency. One man was carrying a loaded gun, and police found weapons, cash and a list of Paris-area Jewish and Israeli associations during the raids.

Paris prosecutor François Molins said all the arrested suspects were French and recent converts to Islam. They were all born in the 1980s or early 1990s. Four of the men involved in the raid had written wills.

"You can imagine what their other plans could have been," counterterrorism official Eric Voulleminot said at a news conference with Molins.

The prosecutor described 33-year-old Sydney, sentenced in 2008 to two years in prison for drug trafficking, as a "delinquent who converted to radical Islam." He said others in the cell indicated they wanted to return to "the land of jihad."

A statement from President François Hollande praised the police for the raids and said the state would continue to "protect the French against all terrorist threats."

Last month's firebombing of the grocery, in a Jewish neighborhood in the Paris suburb of Sarcelles, happened on Sept. 19, the same day a French satirical paper published crude caricatures of the Prophet Muhammad. Anti-Western protests were also growing at the time against an anti-Islam film. One person was slightly injured, but the attack with a Yugoslav grenade came after a summer of what residents described as growing anti-Semitic threats.

"What happened in Sarcelles was just a start, or was just a test," Sammy Ghozlan, head of a French group that tracks anti-Semitism in the country, said. "Islamism is a force of influence and Islamists are going to seek out the weakest people to teach them to kill."

France, which has the largest Muslim population in Europe, is trying to contain the spread of a radical Islam hostile to Western influences. France has made similar anti-terrorism arrests before, only to release the suspects several days later without charges.

The prosecutor was careful not to draw direct links between Saturday's arrests and Mohamed Merah, a young Frenchman of Algerian descent who was killed in a shootout with police in March after his terrorist attacks on the French Jewish community, which has since ramped up security in many parts of the country.

Merah had studied at an Islamist paramilitary camp in Pakistan and claimed ties to al-Qaida. Molins said officials did not believe the men arrested Saturday had trained abroad, but cautioned that the investigation was ongoing.