Zimmerman Protests Heat Up Days After Verdict

July 16, 2013— -- Demonstrations against George Zimmerman's not guilty verdict turned violent in several cities Monday night, prompting police to warn against any further outbreaks as they brace for more demonstrations this week.

The Rev. Al Sharpton said his National Action Network is calling for protests at federal buildings in 100 cities on Saturday, which he is calling "Justice for Trayvon National Day of Action," in order to pressure the federal government to charge Zimmerman with civil rights violations.

Demonstrations flared up immediately Saturday after a Florida jury announced its decision to find Zimmerman not guilty of murdering unarmed black teenager Trayvon Martin last year. The protests, from California to New York and as far away as London, remained peaceful until Monday.

Los Angeles Police Chief Charlie Beck warned residents that police would crack down on violent behavior after 14 individuals were arrested during a protest Monday night.

About 150 individuals splintered off from a peaceful vigil and began running through the streets of Los Angeles smashing vehicles and windows, Beck told ABC News affiliate KABC.

One group stormed into a Wal-Mart and vandalized the store, causing a citywide tactical alert to be declared by police at 9 p.m. More than 300 officers were called in to help subdue the violence, Beck said.

"Parents, don't send your children to protest in and around Crenshaw. Please obey the law," said Beck. "We want this to be a safe event. We want people to get their point across, but we want to keep everybody safe."

Beck warned that Los Angeles cops would be stricter tonight and in coming days if any other protesters gathered in the city.

In Oakland, Calif., nine individuals were arrested after protests there turned violent. Police said that demonstrators had blocked part of a freeway during rush hour, and began to break windows, throw bottles at police officers, spray graffiti messages, and set small fires in downtown Oakland, according to ABC News affiliate KGO in San Francisco.

Across the country, police in Baltimore, Md., are investigating an incident in which a group of young black individuals assaulted a Hispanic man while yelling "This is for Trayvon," according to the Baltimore Sun. A witness reported to police she saw the group attack the man, and threatened to call 911 until they dispersed.

Baltimore police did not immediately return calls for comment from ABC News.

A protest and march in Houston is planned for today, where an increased police presence is on scene.