Supporters of Anonymous have also protested in Dublin and Belfast as the movement takes part in the global protest against corruption on Bonfire Night.
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More than 1.85 million people have called for the US president's visit to be watered down to avoid causing "embarrassment" to the Queen.
Jim Mattis arrived in Baghdad on the day after US-backed Iraqi forces launched an operation to reclaim Mosul from IS.
The scale of the blood poisoning disease sepsis is "far worse" than previously thought thanks to a "crippling" lack of data, a study says.