Imams from countries including France, Belgium, Britain and Tunisia were joined by representatives of other religious communities at the spot where French policeman Xavier Jugele was shot dead in April.
Tour stops will include Berlin -- where organizers say they hope to meet Chancellor Angela Merkel -- Brussels and Nice, with a return to Paris for July 14, the first anniversary of the Nice truck attack.
Islamic State claimed responsibility for the Nice attack when a truck killed 86 people celebrating Bastille Day on the seafront and a truck attack on a Christmas market in Berlin last December that killed 12.
The Imam of Drancy and French writer Marek Halter were behind the initiative of the current tour.
"We are here to say that our religion and the values of Islam are opposed to those assassins," Hassen Chalghoumi, the imam de Drancy, told France Inter radio on Saturday.
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Some 30 people boarded the bus on Saturday with more expected to join on the way bringing the total number of participants to 60.
(Reporting by Johnny Cotton for Reuters TV; Editing by Maya Nikolaeva and Stephen Powe
