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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Seasonal rains have battered the country since late June with more than 150,000 people affected by floods and landslides.
The bus reportedly hit a tree near Russell Square.
Low pressure will throw cloud and few showers across the UK today, but it will also draw in very warm air from Europe again.