Missouri Gov. Jay Nixon on Thursday ordered the state Highway Patrol to take over security in Ferguson, the St. Louis suburb roiled by four nights of unrest over the police killing of an unarmed black teenager.

The governor moved after police came under intense criticism for their handling of the protests, including firing tear gas into crowds on Wednesday night and arresting two reporters.

Nixon said that Ferguson in recent days looked “a little more like a war zone, and that’s unacceptable.”

The head of the Highway Patrol, Capt. Ron Johnson, told reporters: “I understand the anger and fear the residents of Ferguson are feeling, and our police officers will respect both of them.”

Police had said that healing racial tension in Ferguson was a priority. The Ferguson police department is mostly white, while the city is mostly black. Johnson, who is black, grew up in the community.

“It means a lot to me personally that we break this cycle of violence,” he said.

Nixon said that local police would still be involved in patrols, but he said that the Highway Patrol would be in charge. He said that he hoped the change would “provide a breathing space” to address bigger problems....