World leaders expressed shock and horror after a gunman massacred 20 small children and six teachers Friday in the US state of Connecticut, in one of the worst school shootings in history.
UN chief Ban Ki-moon wrote to Connecticut Governor Dan Malloy to give his "deepest condolences at the shocking murders," a statement said.
"The targeting of children is heinous and unthinkable," he added in condemning the "horrendous" crime.
European Union diplomacy chief Catherine Ashton expressed "shock" at the "tragic shooting."
The head of the European Commission Jose Manuel Barroso spoke of his "deep shock and horror" upon hearing of the massacre at Sandy Hook Elementary School, which he called a "terrible tragedy."
"Young lives full of hope have been destroyed," he said in a statement.
There were almost no non-fatal injuries, indicating that once targeted, there was rarely any chance of escape, and that the gunman, believed to be 20-year-old Adam Lanza, was unusually accurate or methodical in his fire.
"The news is just awful. The thoughts and prayers of Canadians are with the students and families in CT affected by this senseless violence," Canadian Prime Minister Stephen Harper wrote on his Twitter account.
His Foreign Minister John Baird said Canadians "stand shoulder to shoulder with our American friends at this difficult time."
The child victims were reported to be aged between five and 10.
"I was shocked and deeply saddened to hear about today's horrific shooting," British Prime Minister David Cameron said.
"My thoughts are with the injured and those who have lost loved ones. It is heartbreaking to think of those who have had their children robbed from them at such a young age, when they had so much life ahead of them."
Britain's Queen Elizabeth II sent a message to President Barack Obama in which she said she was "deeply shocked and saddened" to hear of the shootings.
"The thoughts and prayers of everyone in the United Kingdom and throughout the Commonwealth are with the families and friends of those killed and with all those who have been affected by today's events."
French President Francois Hollande also extended his condolences to the victims and their relatives in a message to Obama.
"This news... horrified me and I wish to express my deep shock and consternation," Hollande said.
The foreign ministry also issued a message in which it offered "France's full support to the American people and authorities."
Mexico's newly inaugurated president, Enrique Pena Nieto, also expressed his support to the US after the deadly shooting.
"My solidarity with the American people and President @BarackObama after the tragedy this morning in Connecticut," he wrote on Twitter.
And Australian Prime Minister Julia Gillard said "Australia grieves with America today following the mass shooting of primary school children and teachers in Connecticut.
"Like President Obama and his fellow Americans, our hearts too are broken.
"We share America's shock at this senseless and incomprehensible act of evil."