FERGUSON, Mo. » More than a dozen people protesting a grand jury’s decision not to indict the police officer who fatally shot 18-year-old Michael Brown have been arrested outside of the Ferguson police department.

Tensions escalated late Friday during an initially calm demonstration after police said protesters were illegally blocking West Florissant Avenue.

Missouri Department of Public Safety spokesman Mike O’Connell tells the St. Louis Post-Dispatch 15 people were arrested.

The demonstration in Ferguson came after protesters earlier in the day temporarily shut down three large malls in suburban St. Louis.

Chicago, New York, Seattle and Northern California also saw demonstrations Friday.