This is a phenomena of mob violence which has been stoked up by individuals and social media.
PSNI Chief Constable Matt Baggott added it was fortunate nobody had been killed or seriously injured last night, and he praised police for doing a "magnificent" job.
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It will be warm and sunny in much of the UK with a risk of heavy, thundery showers for parts of central and southern England and Wales.
Ariana Grande, who had been performing at the Manchester Arena when the bombing happened, tweeted a message of support for those affected.
Berlinah Wallace was convicted of throwing a corrosive substance with intent but acquitted of murder.