The United Kingdom raised its threat level to "critical" from "severe" late Tuesday, a day after a suspected terrorist exploded a bomb at a Manchester arena, killing more than 20 concertgoers. U.K. Prime Minister Theresa May placed the country on the highest state of alert, meaning officials believe that another attack is expected "imminently," after authorities have yet to rule out whether suicide bomber Salman Abedi acted alone. Monday's attack took place following the close of an Ariana Grande concert in Manchester, killing 22 and injuring dozens of others.
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