PARIS - Government officials and Jewish leaders are concerned the conflict in Gaza may spill over into violence in Europe, with attacks reported against Jews and synagogues in France, Sweden and Britain.

Assailants rammed a burning car into the gates of a synagogue in Toulouse, in southwest France, Monday night.

A Jewish congregation in Helsingborg, in southern Sweden, was attacked Monday night by someone who "broke a window and threw in something that was burning," said police spokesman Leif Nilsson. And on Sunday slogans, including "murderers ... You broke the cease-fire," were daubed on Israel's embassy in Stockholm.

In Denmark, a 27-year-old Dane born in Lebanon to Palestinian parents is alleged to have injured two young Israelis last week in a shooting police suspect could be linked to the Gaza crisis. Belgium ordered police in Antwerp and Brussels to be on increased state of alert" Tuesday after recent pro-Palestinian protests ended in violence and arrests.

France has Western Europe's largest Jewish and Muslim communities and a history of anti-Semitic violence flaring when tensions in the Middle East are high. In 2002, some 2,300 Jews left France for Israel because they felt unsafe. Even in normal times, anti-Semitic incidents are not uncommon.

President Nicolas Sarkozy warned in a statement Tuesday that France would not tolerate violence linked to the Gaza crisis. A day earlier, his interior minister said she was concerned about the prospect of contagion and met with the heads of the two main Muslim and Jewish groups and police officials to stress the need to "preserve national unity."

Damage to the synagogue in Toulouse was limited to a blackened gate. Police said unlighted gasoline bombs were found in a car nearby and in the synagogue's yard. A local Jewish leader, Armand Partouche, said he believed the assailants fled when the building's alarm went off.

Local authorities promised Tuesday to boost security for synagogues and other Jewish sites in the city, Partouche said.

"We really fear that anti-Semitism will spring up again and that the current conflict will be transposed to our beautiful French republic," Partouche said.

French Muslim leader Mohammed Moussaoui condemned the attack, saying no motive could justify an assault on any place of worship.

Interior Ministry spokesman Gerard Gachet said police have not noted an increase in violence against Jews linked to the Gaza crisis. But he said tensions are likely.

In Britain, the Community Security Trust, a Jewish defense group, said it had seen a rise in anti-Semitic incidents since the start of Israel's offensive against Gaza. The group said it recorded 20-25 incidents across the country in the past week -- a sizable increase from 2-3 incidents usually reported to the group over the Christmas-New Year period.

Police are investigating an arson attempt Sunday on a synagogue in north London. Assailants splashed liquid on the door and set it on fire. Police would not speculate on whether the attack was linked to the Gaza crisis.

In another incident last week, a gang of 15-20 youths walked along the main street in Golders Green, a largely Jewish neighborhood in north London, shouting "Jew" and "Free Palestine" at passers-by, said Community Security Trust spokesman Mark Gardner.