Missouri governor declares state of emergency ahead of Ferguson grand jury decision
Police officers arrest a demonstrator on August 18, 2014 in Ferguson (AFP)

Missouri Gov. Jay Nixon on Monday declared a state of emergency ahead of a grand jury decision about the fatal police shooting of an unarmed black man.

The governor's executive order, which activated the National Guard, noted that "the City of Ferguson and the St. Louis region have experienced periods of unrest over the past three months."

The grand jury is expected to decide this month whether Ferguson police officer Darren Wilson should face charges in the death of 18-year-old Michael Brown.

"Regardless of the outcome," the executive order states, "there is the possibility of expanded unrest."