"There is an urgent need for all the communities in Rochdale to work together, to tackle this heinous crime."
"Our young children from our borough were abused - and we all have a collective responsibility to ensure we do the best to safeguard our children."
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The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
In her message Theresa May praised the "inspirational bravery" and "unbreakable spirit" of Mancunians in the wake of the blast.