Obama on Boston Marathon explosions: "We will get to the bottom of this, and we will find out who did this, we'll find out why they did this."

U.S. President Obama pauses as he remarks on Boston bombings. PHOTO/Mark Wilson/Getty Images

(Reuters) - President Barack Obama vowed on Monday that the United States will find out who carried out explosions in Boston and will hold them accountable, and a White House official said the twin blasts are being treated as an "act of terror."

"We still do not know who did this or why, and people shouldn't jump to conclusions before we have all the facts," Obama said in a televised

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