Several thousand demonstrators walked calmly through the streets of Paris behind a large banner that read "Total Support for the Struggle of the Palestinian People".
But clashes erupted at the end of the march on Bastille Square, with people throwing projectiles onto a cordon of police who responded with tear gas.
The unrest continued early Sunday evening as police announced six arrests had been made.
A small group tired to break into two synagogues in central Paris, a police source told AFP.
Riot police dispersed the group, with two members of the Jewish community and six officers slightly injured in the ensuing scuffle, the source said.
Prime Minister Manuel Valls condemned the attempted synagogue stormings "in the strongest possible terms".
"Such acts targeting places of worship are unacceptable," he said in a statement.
"I am profoundly shocked and revolted. This aggression towards the Jewish community has taken an absolutely unacceptable turn," Joel Mergei, president of the Israelite Central Consistory of France, told AFP.
Paris Mayor Anne Hidalgo called for "calm in the face of tensions" in the Middle East.
In the northern city of Lille, meanwhile, between 2,300 and 6,000 people protested peacefully, according to differing figures provided by the police and organizers.
The descent into violence in the Gaza Strip began on June 12th when three Israeli teenagers were kidnapped and later murdered, triggering a major military crackdown on Hamas in the West Bank and an escalation of rocket fire from Gaza.
The brutal revenge killing of a Palestinian teenager by Jewish extremists on July 2nd added further fuel to the fire, turning into an all-out conflict on July 8th when Israel launched an air campaign against Gaza militants.
The Palestinian death toll from Israel's punishing air campaign has hit 168.
So far, no Israelis have been killed, although militants in Gaza have pounded the country with about 715 rockets since the fighting began, around 160 of which have been intercepted by the Jewish state's Iron Dome defence system.
"I came to say no to this massacre," Amid Hamadouch, 30, told AFP at the Paris protest while it was still peaceful, with a sticker reading "Boycott Israel, Racist State" on his jacket.
"They are bombing innocent people. There are missiles being launched by Hamas, but the Israeli response is disproportionate. They are attacking the civilian population and not Hamas officials."
The crowd, very young, shouted slogans such as: "We Are All Palestinians!" and "Only One Solution, End the Occupation!".
Many protesters carried banners on which they had stuck photos taken from the internet, reportedly showing Palestinian children killed or injured, houses razed to the ground or clouds of smoke emerging from bombed districts in Gaza.
According to the UN Office for the Coordination of Humanitarian Affairs, a majority of those killed in Gaza so far -- 70 percent -- have been civilians, of whom 30 percent were children.