Russian leader Vladmir Putin has called the shootings in a school in Connecticut "particularly tragic" as the majority of the 28 killed were children.
The Kremlin said in a statement:
Vladimir Putin asked Barack Obama to convey words of support and sympathy to the families and friends of the victims and expressed his empathy with the American people.
More top news
Facebook says it will start test flights later this year of a solar-powered drone that aims to provide remote areas with the internet.
Children's charity Kids Company is being investigated by the Metropolitan Police over criminal allegations.
A senior employee at a 4-star London hotel has been jailed for six years for raping a man who he lured to a fake job interview.