Police will work to protect peaceful protesters after a grand jury's decision in the Michael Brown shooting case is announced, but those who cross the line into violence will face consequences, Missouri Gov. Jay Nixon warned Tuesday.

More than 1,000 police officers have received special training ahead of a decision expected later this month about whether Ferguson Officer Darren Wilson, who is white, will face criminal charges for fatally shooting Brown, 18, who was black and unarmed.

The National Guard will be available if needed and a unified command of state, St. Louis city and St. Louis County police will provide security for protests.

At a news conference with law enforcement officials to outline preparations, Nixon recalled violent protests that occurred soon after Brown was killed in August.

"That ugliness was not representative of Missouri and it cannot be repeated," he said.

Weeks of protests followed the shooting and some of the unrest included looting and rioting. Many businesses along West Florissant Avenue in Ferguson, a St. Louis suburb, still have boards on their windows.

During the first days of mostly peaceful protests, police donned riot gear and patrolled in armored vehicles, drawing widespread criticism and raising questions about a program that supplies surplus military equipment to local police departments.

A small number of protesters attacked squad cars, tossed molotov cocktails at officers and, in a few cases, shot guns in the direction of police, who responded with tear gas, smoke canisters and rubber bullets. On many nights, dozens were arrested.

St. Louis County police initially handled security, but criticism of their tactics prompted Nixon to put Highway Patrol Capt. Ron Johnson in charge. He and other police leaders said the response was necessary to protect officers, protesters and the public.

This time around, officers have undergone a combined 5,000 hours of training and police leaders have reached out to civil rights and protest groups to urge cooperation. Last week, a coalition representing more than 50 activist groups asked St. Louis County prosecutor Bob McCulloch for 48 hours' notice before a grand jury decision is announced, saying that will allow them to help prevent violence.

But some organizers fear police will be heavy handed after the grand jury announcement.

Ashley Yates of St. Louis, co-creator of the group Millennial Activists United, noted that the vast majority of protests have been peaceful and said Nixon should focus on addressing the systemic problems faced by minority communities, "not reactionary policing techniques."

Organizers of her group and other protesters gathered Tuesday for training that includes how to take notes and shoot video of police actions on the streets.

"There is a significant effort to make sure that people's rights are protected and that there's no violence on either side," said Andy Stepanian, a spokesman for several protest groups.

The Rev. Al Sharpton, who has spent time with Brown's family and called for a federal prosecution of Wilson, slammed Nixon's remarks, saying he was ignoring the underlying issues in the case.

"For the governor to denounce the violence and ugliness and not address the militarization of Ferguson in August, including policemen wearing armbands supporting the policeman who killed Michael Brown, and selective leaks of grand jury testimony that could taint the decision of this grand jury, is questionable on all accounts," he said in a statement.