Two bomb blasts struck one of America's top sporting events on Monday, killing at least three and wounding more than 100 as the Boston Marathon erupted in a maelstrom of blood, screams, smoke and panic.
The twin explosions 13 seconds apart came more than a decade after nearly 3,000 people were killed in suicide airliner strikes on New York, Washington and Pennsylvania on September 11, 2001.
Act of terror?
President Barack Obama went on national television to warn against "jumping to conclusions" but a senior White House official, speaking on condition of anonymity, said such an attack was "clearly an act of terror."
Special agent Rick DesLauriers, who heads the Federal Bureau of Investigation’s (FBI) Boston bureau, told reporters: "It is a criminal investigation that is a potential terrorist investigation."
Security was stepped up in major cities across the United States amid fears of a repeat of the September 11 attacks. Obama said those behind the blasts will "feel the full weight of justice."
At the blast scene, a horrific chorus of high-pitched wailing and screaming rang out as bewildered runners and spectators fled the carnage and debris. An eight-year-old boy was reportedly among the dead. The Boston Globe identified him as Martin Richard, whose father William was running in the race. His mother and a sister were gravely injured while a second sister was unharmed. More than 100 people were wounded, Massachusetts governor Deval Patrick said, without giving an exact figure. The Globe said more than 140 were hurt.