A dozen Syrian-Americans opposed to President Bashar al-Assad got the event off to a slow start in New York's Dag Hammarskjold Plaza, an hour later than advertised on Facebook.
The names of 100,000 of the more than 160,000 people killed during the three-year civil war will be read during a 24-hour period in cities across North America, Europe and inside Syria, they said.
Demonstrators held up a banner that read: "Over 160,000 dead in Syria. How many more? #100000Names," with US and Syrian opposition flags as the New York traffic rumbled past.
"Over 160,000 dead in Syria. How many more?"
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Sharp divisions between China and Russia, which have vetoed four resolutions on Syria, and Western powers have paralyzed Security Council efforts to find a solution to the brutal conflict.
Activists said they chose the location so the Security Council could "see the results of their inaction."
"It's very painful for us to know that we're going to wake up tomorrow and have Bashar al-Assad be president for another seven-year term," activist and writer Lina Sergie Attar told AFP.
"The dead, the displaced, the raped, the maimed. All of these are the accomplishments of this man who wants to declare himself president yet once again and that's what we're protesting."
The names will be shared between, and read out by activists staging similar events in New York, London, Toronto, Chicago, Los Angeles, Berlin, Frankfurt, Paris and in Syria, she said.