CHICAGO >> Thousands of mostly peaceful pro-Palestinian protesters marched in Chicago on the opening day of the Democratic National Convention on Monday, in a show of force against the Biden administration’s support for Israel in the Gaza war.

After hours of peaceful demonstrations, dozens of protesters broke through part of the perimeter security fence, drawing riot police to the site, a Reuters witness said.

The DNC’s security team confirmed that protesters breached a portion of the fencing on the outer perimeter near the convention arena but said law enforcement personnel acted quickly and at no point was there a threat to any attendees.

Reuters witnesses saw four people detained and placed in handcuffs. The DNC’s security team did not respond to a request for comment on whether those protesters were arrested.

Chanting intensified ahead of the fence breach, as protesters reached a neighborhood park on Chicago’s West Side and paused to amplify their calls for a ceasefire. Amid the noise, the crowd turned its frustration toward Vice President Kamala Harris, referring to the Democratic candidate as “Killer Kamala”.

Chicago police formed a perimeter around the park on foot to contain protesters, with some police personnel on bikes.

Still, the umbrella group “March on the DNC” drew fewer supporters than expected to a park outside the convention arena, hours before President Joe Biden was to address the gathering.

They started a one-mile march near where Democratic delegates will nominate Harris as their candidate to face Republican Donald Trump in November’s presidential election.

Organizers had expected tens of thousands of protesters – enough to fill the park and the march route – Hatem Abudayyeh, a spokesman for March on the DNC, said early Monday. By afternoon though, several thousand protesters had gathered for speeches and the park was only half full.

The coalition of more than 200 groups includes those advocating for a variety of causes from reproductive rights to racial justice. Many people were coming from Palestinian and Arab communities in Illinois and neighboring states, organizers said last week.

Roman Fritz, at 19 one of the youngest Wisconsin delegates, wore a scarf imprinted with the traditional Palestinian keffiyeh pattern. He said he supported Harris as the party nominee to beat Trump.

Dozens of Muslim delegates and their allies, angry at U.S. support for Israel’s offensive in Gaza, are seeking changes in the Democratic platform and plan to press for an arms embargo, putting the party on guard for disruptions to high-profile speeches at the convention.

Some protesters were doubtful that the party will change its platform.

“It’ll never happen,” said Mwalimu Sundiata Keita, who traveled from Cincinnati, Ohio, to join the protest. “It’s the policy of the party to support Israel, and until that policy changes, that’s the way it’s going to be.”

Another large protest was scheduled for Thursday, when Harris is due to formally accept the nomination.

Pro-Palestinian groups have for months protested the Biden administration’s military and financial support for Israel in its war against Hamas, which has killed more than 40,000 Palestinians in Gaza, according to Gaza health officials.

Israel launched the offensive after it was attacked on Oct. 7 by Hamas militants who killed 1,200 people, according to Israel tallies.

The protests swelled on U.S. college campuses in the spring, with police clearing student encampments, at times after confrontations between protesters and counterprotesters.

“The Democrats are the ones in power,” Abudayyeh said on Monday. “It’s their war. They’re responsible for it, they’re complicit, and they can stop it.”