Missouri Governor Jay Nixon is again banking on the National Guard to keep order in the town of Ferguson, where three months ago, white police officer Darren Wilson gunned down black teenager Michael Brown, in a case that has led to successive nights of protests, some leading to violent confrontation between police and protesters in Ferguson and elsewhere.

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The grand jury is expected to hand down its decision in mid-November, raising tensions in the predominantly black neighborhoods of Ferguson and adjacent towns. State officials says they anticipate a show of anger when the decision comes out. Some of the protesting groups have reacted to the National Guard activation saying it was premature and antagonistic.

Governor Nixon called in the National Guard in August but its role was limited to protecting a police command post. Nevertheless, it drew sharp criticism from demonstrators who said it was another indication that law enforcement preferred a military-style approach to the  problem.

The Guard pulled out after a few weeks without incident.

This time, the activation order will last for 30 days.

"As part of our ongoing efforts to plan and be prepared for any contingency, it is necessary to have these resources in place in advance of any announcement of the grand jury's decision," Mr. Nixon said in a written release.

He went on further to say the National Guard will still secure command posts, fire stations and other critical locations, and will perform other tasks that will free up law enforcement personnel who can then focus on community policing.

The order gives the Missouri adjutant general responsibility to decide how big the military deployment will be.

St. Louis Mayor Francis Slay said he supported the governor's decision, but clarified the troops will have a secondary role in maintaining peace and order.

"The Guard will not be used on the front lines," Mr. Slay said.

Mayor Slay said Guard personnel might be stationed around shopping centers, strip malls and government buildings.