CHICAGO (AP) — Thirteen people were arrested during protests on the first day of the Democratic National Convention in Chicago, most of them in connection with a “brief breach” of the security fence “within sight and hearing of the United Center,” the city’s police chief said Tuesday.

More protests were planned throughout the week, including one outside the Israeli consulate on Tuesday evening, but the turnout at the main rally on Monday was far below organizers’ estimates of more than 20,000 participants.

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Chicago Police Chief Larry Snelling said Tuesday the crowd consisted of about 3,500 people and the vast majority of protesters were peaceful.

However, some clashed with police, using pepper spray against them and throwing water bottles at officers during the confrontation in the park, where there was a gap in the security fence, Snelling said. He said officers did not use chemical sprays.

“Our officers have shown great restraint,” he said at a press conference. “We will not tolerate vandalism and violence in our city. … We will continue to protect the city.”

Snelling said that with more protests planned, his department is prepared to de-escalate situations whenever possible.

“We are up to this challenge,” said Snelling. “The city is up to this challenge.”

The park where most of the arrests took place is a block from the convention grounds and was the target of a march of thousands demanding a ceasefire in the war between Israel and Hamas. Several dozen activists broke away from the main group, broke through the fence and were pushed back by police.

Authorities said the internal security perimeter around the United Center had not been breached and there was no danger to convention attendees.

On Tuesday morning, additional fencing was erected in the park and high metal barriers were reinforced to prevent protesters from lifting and removing the panels. There were no police or protesters in the park early Tuesday.

The 13 people arrested during Monday’s protests were held on charges ranging from trespassing, resisting justice and obstruction of justice to aggravated assault against police officers, Snelling said.

At least ten of them were arrested in connection with the fence, he said.

Snelling said he did not associate those who tore down the fence with the entire march. He said the vast majority of participants were peaceful, and he praised his officers’ conduct in that moment.

The Chicago chapter of the National Lawyers Guild said two of those arrested were hospitalized. Snelling said they were not taken to the hospital because of their injuries, but “to provide them with the necessary treatment related to their medications.”

In addition, two people were arrested for property damage and resisting state authority during a protest march on Sunday evening. By Tuesday morning, 15 people had been arrested.

In downtown Chicago, there was tighter security than usual – including police officers with guns slung across their bodies – outside the office building that houses the Israeli consulate and a major transportation hub for the city. Metal barricades were erected and an official said they were preparing for a 7 p.m. demonstration.

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The consulate is about two miles from the United Center and has been the scene of numerous demonstrations since the Gaza war began in October. It is housed in a building connected to the Ogilvie Transportation Center, a major commuter rail station.

Israel supporters, including some relatives of people kidnapped by Hamas, gathered at a pro-Israel art installation near the consulate on Tuesday to call on the U.S. government to continue to support Israel and work for the release of the hostages. The art installation included giant milk cartons with photos of some of the hostages.

Elan Carr, CEO of the Israel-American Council, condemned the pro-Palestinian protesters who descended on Chicago this week, calling them “fringe lunatics” and demanding that U.S. leaders stand “clearly with the State of Israel.”

Most of the largest demonstrations were organized by the March on the DNC coalition, which advocates for a ceasefire in Gaza, but smaller protests also took place throughout the city during the convention’s welcome party at Navy Pier.