Barack Obama has tweeted on the White House's official Twitter account:
20 beautiful children & 6 remarkable adults. Together, we will carry on & make our country worthy of their memory. -bo #MomentForSandyHook
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The singer, 31, said on Twitter that she and her partner Jonathan Powell were grieving their loss.
A fine evening ahead to the south with some late sunshine in places.
Prince Charles and the Duchess of Cornwall have visited Manchester Arena, the site of a suicide bombing in May which left 22 people dead.