President Barack Obama ordered the "full resources" of the federal government to respond to the tragic and "senseless" Boston Marathon bombing today.
He also called for security around the U.S. as necessary.
At least two are dead and 110 injured after a explosions rocked downtown Boston near the finish line of the annual sporting event Monday afternoon.
Some sources have reported the toll even higher.
"We still do not know who did this or why," Obama said from the White House. "But make no mistake, we will get to the bottom of this, and we will find out who did this."
Any individuals or groups responsible will "feel the full weight of justice," he said, while the American people will say a prayer for Boston tonight."
Notably absent from his three-minute remarks was the word "terror," though federal investigators are classifying the bombings as a terrorist attack.
It is not clear if the attack came from a domestic or foreign source.
In any case, Obama did not go there, at least not yet.
"Today is a holiday in Massachusetts, Patriot's Day," he said.
"It's a day that celebrates the free and fiercely independent spirit that this great American city of Boston has reflected from the earliest days of our nation."
"It's a day that draws the world to Boston's streets in a spirit of friendly competition," he added. "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."
Afterward, a White House official said "any event with multiple explosive devices - as this appears to be - is clearly an act of terror, and will be approached as an act of terror."
"However, we don’t yet know who carried out this attack, and an investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic."