President Barack Obama, responding to the explosions at the Boston Marathon, says the United States does not know "who did this or why" but vowed that whoever is responsible "will feel the full weight of justice."
He said: "We will find out who did this and we will hold them accountable."
Obama made his remarks Monday evening from the White House about three hours after two explosions detonated near the marathon's finish line. At least two people were killed and 50 injured in the blasts.
"The American people will say a prayer for Boston tonight. And Michelle and I send our deepest thoughts and prayers to the families of the victims in the wake of this senseless loss," said Obama. "We don??t yet have all the answers. But we do know that multiple people have been wounded, some gravely, in explosions at the Boston Marathon."
Obama has been in touch with federal law enforcement and Massachusetts officials in the aftermath of the explosions.
"We still do not know who did this or why. And people shouldn't jump to conclusions before we have all the facts. But make no mistake -- we will get to the bottom of this. And we will find out who did this; we'll find out why they did this. Any responsible individuals, any responsible groups will feel the full weight of justice," said Obama.
The Secret Service reacted cautiously to the blasts, expanding the security perimeter around the White House.
"Boston is a tough and resilient town. So are its people. I'm supremely confident that Bostonians will pull together, take care of each other, and move forward as one proud city. And as they do, the American people will be with them every single step of the way," said Obama.