The French president has promised the Jewish community a major increase in security after police shot dead a man suspected of targeting a kosher shop.
Francois Hollande said there would be "total mobilisation of the state to fight all terrorist threats".
A suspected radical Islamist, believed to have thrown a grenade at a kosher grocery in Paris last month, died in a raid in Strasbourg on Saturday.
Hours later, blank bullets were fired outside a Paris synagogue.
Services marking the Jewish festival of Sukkot were cancelled on Saturday night after eight shots were heard outside the synagogue in the Argenteuil area of the capital.
Jewish community leaders linked the incident to a series of raids across France by anti-terror police in which one man died and several other people were arrested.
A 33-year-old Muslim convert identified as Jeremy Louis-Sidney, who had a conviction for drug-trafficking, was shot dead when police entered his Strasbourg flat and said he opened fire on them with a .357 Magnum revolver.
Another 11 suspects were detained on Saturday in raids in Cannes, Nice and elsewhere, which Prime Minister Jean-Marc Ayrault said were aimed at "dismantling terrorist networks".
According to prosecutors, Jeremy Louis-Sidney's fingerprints had been found on the remains of the grenade thrown at a kosher shop in Sarcelles, a Jewish area of Paris, on 19 September.
Interior Minister Manuel Valls spoke of an anti-Semitism "in our neighbourhoods and suburbs", adding that the threat "does not appear to come from foreigners, it appears to be French converts".
"There is a highly noticeable resurgence of anti-Semitic attacks and aggression," community spokesman Moshe Cohen-Sabban told French radio.
President Hollande, after a meeting with two representatives of France's Jewish community, said that security would be beefed up in the coming days.
He also spoke to the head of the French Council of the Muslim Faith, Mohammed Moussaoui. The country's Muslims were also victims of radical Islam, Mr Hollande said.
In March, French Islamist Mohamed Merah murdered three Jewish schoolchildren, a rabbi and three paratroopers in and around Toulouse before being shot dead in a police siege of his flat.