Kevin Johnson

USA TODAY

CLEVELAND – Police Chief Calvin Williams issued a warning Tuesday to an undisclosed number of loosely-affiliated masked protesters who have triggered unusual anxiety among visitors and local residents with their unplanned appearances across the city: "If you are a member of a group that causes you to have to hide your face, then you probably need a different cause."

Protests outside the Republican National Convention have been peaceful, but police have received at least a dozen calls so far related to concerns about the small groups of black-clad anarchists who often don masks during demonstrations and other protests.

Following some of the calls, Williams said, officers have recovered slingshots and gas masks, both banned from the downtown event zone for the duration of the convention. That has prompted concerns about the group's intentions, Williams said.

"If you have a different issue (other than participating in peaceful protests), then we've got a problem," the chief said during a Tuesday morning briefing.

The pop-up groups, though small in number, appear to be the only disrupting force in a so-far uneventful series of protests that marked the convention's opening.

About 500 protesters, including some gun-toting gun rights activists, participated in marches or rallies during the first full day of the convention -- far fewer than the numbers predicted by protest group organizers.

Protesters carry guns, decry Trump as RNC opens

The activities have resulted in only a handful of arrests, including three early Tuesday related to anti-fracking and immigration rights causes. The suspects, all charged with criminal mischief, scaled flagpoles outside the Rock & Roll Hall of Fame to hang a large banner reading: “Don’t Trump our communities.”

Photos posted online by the activists show two figures in helmets and climbing gear going up the poles and unfurling the banner, which included messages reading “ban fracking,” “tear down the wall” and “stop climate injustice.”

The demonstration took place around 7 a.m. – hours before the Hall of Fame opened and at a time when few people were present.

Photos indicate police arrived on the scene within moments, and by 9 a.m., the banner had been removed.

Jason Noble of the Des Moines Register contributed to this story.