Thousands of people protested against Israel and in support of residents in the Gaza Strip, where a six-day conflict has left 168 Palestinians dead.
Some 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.
Police announced six arrests had been made, after a small group tired to break into two synagogues in central Paris, a police source told AFP.
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 organisers.
The descent into violence in the Gaza Strip began on June 12 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 Jews on July 2 added further fuel to the fire, turning into an all-out conflict on July 8 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.
“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.