Demonstrations in support of civilians beaing heavy shelled by the government in the rebel-held neighborhoods of Aleppo spread to 27 cities across the globe over the weekend.

Nearly 200 civilians have been killed by Russian-backed government shelling in the opposition-held half of the divided city since April 19, including hospital personnel, rescue workers and children.

It started with a Facebook post. On Friday morning, a Facebook event was created by a group of Syrian activists calling for a worldwide protest against the targeting of civilians who have been subject to continuous government attacks. The organizers hoped the event would generate a widespread response that would persuade global powers to pressure Bashar al-Assad’s government and its Russian allies to stop bombarding civilian areas in rebel-held Aleppo, Syria’s largest city and a place of vital strategic importance to opposition forces and the government alike.

“We started the Facebook event on Friday morning, and by Saturday, people organized protests and sit-ins in multiple cities,” said journalist Sarah Dadouch, a member of the Syria Pressure Advocacy Group (SPAG), who organised the event.

The movement quickly gained momentum as many Syrian and international Facebook users changed their profile pictures to a red square on Friday in support of the page. A Twitter hashtag – #AleppoisBurning – was also created. Within 24 hours of creating the event, some 5,000 people had expressed interest in attending. By Saturday morning, dozens of similar, location-specific pages had sprung up in cities across the world, including New York City, Brussels and Paris.

“At first, we created chat rooms and private groups where we discussed the technicalities of the demonstrations, but by Saturday, the event got so big that it was nearly impossible to keep track of it,” she added.

“But despite the large number of events organized, they all fell under one red banner of solidarity for Aleppo.”

SPAG was formed only days earlier by a group of Syrian activists and journalists with the aim to serve as a mediator between Syrian activists worldwide who wanted to plan solidarity demonstrations.

The group consisted of Deiaa Dughmoch, Rami Jarrah, Sarah Dadouch, Kousay Hayani, James Sadri and Bissan Fakih.

On Saturday morning, SPAG issued a press release addressed to world leaders that outlined the common principles of the protests, including a condemnation of the Assad government for its “war crimes against humanity” and a demand for world powers to offer humanitarian protection to civilians. Demonstrators demanded that government blockades around rebel-held areas be lifted and humanitarian aid be delivered to all besieged areas in Syria.

Red placards were raised in European cities such as Paris, Berlin, Brussels, Milan, Oslo and Leeds, with many more planned over the next few days.

In the U.S., people gathered in Washington D.C., Chicago, New York, Boston and San Francisco. “Each country organized its own independent event, but they all fell under the umbrella of a worldwide protest,” said Dadouch.

Further protests are set to take place this week in Gaza, Amsterdam, Antwerp, Prague, London and Barcelona.

“The reason why this event was successful, unlike others that failed to gain international compassion, is because people are seeing what’s happening in Aleppo, and the brutal way civilians are being killed by the government,” said Dadouch.