By Steve Holland and Jeff Mason
WASHINGTON (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 statement. "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."
Obama did not call the explosions an attack and emphasized that much was not known about them. But a White House official said any event with multiple explosive devices, as the Boston episode appeared 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 a thorough investigation will have to determine whether it was planned and carried out by a terrorist group, foreign or domestic," the official said.
The Boston explosions put the White House on edge with the Secret Service raising security around the executive mansion. Obama said he has directed the federal government to increase security around the United States as necessary after the explosions.
The blasts offered a fresh challenge to Obama, who early in his second term has been focused on domestic agenda topics such as gun control, immigration and budget deficits.
Obama quickly shifted into a national security mode as soon as he was told about the Boston blasts at 3 p.m. EDT (8:00 p.m. British time).
He called Boston Mayor Tom Menino and Massachusetts Governor Deval Patrick and offered federal assistance. Obama was briefed by FBI Director Bob Mueller and Homeland Security Secretary Janet Napolitano.
"We will find out who did this and we will hold them accountable," Obama said.
He called Boston a tough and resilient town.
"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," he said.
Separately, Vice President Joe Biden, in a telephone conference call about proposals to tighten gun laws, offered his prayers as he reacted to images he saw on television from Boston.
"As I'm speaking here, they just turned on the television here in my office. Apparently there has been a bombing. I don't know any of the details about what caused it, who did it. I don't think it exists yet," Biden said.
"But our prayers are with those people in Boston who have suffered injury. I don't know how many of them there are. I'm still looking at it on television now," he said.
Biden was speaking off the cuff and did not appear to have any independent knowledge of what caused the explosions.
(Reporting by Steve Holland and Jeff Mason; Additional reporting by Roberta Rampton; Editing by Eric Walsh and Eric Beech)