Aerial footage from the NBC television network has revealed the scale of the damage caused by a tornado that flattened communities and claimed at least six lives in the US Midwest.
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The talks descended into crisis on Friday when Canada's trade minister Chrystia Freeland walked out of meetings.
Police in New York are still investigating what the substance is and whether it could be harmful.
The Sherlock actor made the comment while he received an award for his humanitarian work.