The principal of Columbine High School has offered his condolences to the families of the victims killed during a school shooting in Newtown, Connecticut.
"It's a reminder of how vulnerable we are as a society," he said.
"As a society we have to come together, we have to stop these senseless deaths." reports the Denver Post.
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The chancellor now faces the prospect of forming a minority government or calling for a snap election.
The 73-year-old said a return is unlikely "given the politicised atmosphere that seems to have afflicted our set."
Chancellor Philip Hammond said the UK will make a financial proposal to the EU in the next three-and-a-half weeks.