A police officer aims his weapon at a demonstrator protesting the shooting death of teenager Michael Brown, in Ferguson, Missouri August 13, 2014. [Photo/Agencies]

FLORISSANT, Missouri - Missouri state police will take over supervising security from local police in the St. Louis suburb that's been the scene of violent protests since a white police officer fatally shot an unarmed black teenager, the governor announced Thursday. A new protest with hundreds of people began hours later.

President Barack Obama has appealed for "peace and calm" on the streets of Ferguson, the predominantly black city where crowds have gathered to protest since Saturday's shooting of 18-year-old Michael Brown.

Gov. Jay Nixon announced that state Highway Patrol Capt. Ron Johnson, who is black, will take over security after the local police response drew heavy criticism. Nixon said the change is intended to make sure "that we allow peaceful and appropriate protests, that we use force only when necessary, that we step back a little bit and let some of the energy be felt in this region appropriately."

Johnson said he grew up in the community and "it means a lot to me personally that we break this cycle of violence."