Tags: Eric Holder

National Guard troops and police aimed to head off a third night of violence on Wednesday in Ferguson, Missouri, as more than 400 people have been arrested in the St. Louis suburb and around the United States in civil unrest after a white policeman was cleared in the killing of an unarmed black teenager.

Missouri's governor ordered hundreds more National Guard troops on Tuesday to the St. Louis suburb rocked by rioting after a white policeman was cleared in the fatal shooting of an unarmed black teenager, while the local mayor said the governor did not do enough to protect businesses from looting.

Violence flared again in the St. Louis suburb of Ferguson on Monday, with gunshots heard and tear gas fired, after a Missouri grand jury decided not to indict a white police officer over the fatal shooting of an unarmed black teenager in August.