Police in Ferguson in Missoury is firing smoke canisters at protesters after a midnight curfew has been broken.
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In its first response since the 22-year-old's death, North Korea said Mr Warmbier was treated "according to international standards".
Police would face "real challenges" tackling a repeat of the London riots after years of cuts, one of Britain's most senior officers warns.
Here are the buildings we know are affected and what action is being taken by local authorities.