The Thai island of Koh Phangan, where 22-year-old Stephen Ashton is believed to have been killed in crossfire between rival gangs, is a popular party destination for tourists.
It is famous for its monthly Full Moon parties on Haad Rin Beach which draw thousands of tourists, especially at this time of year.
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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.