The explosions hours into the 117th running of the iconic 26.2-mile race came well after the elite runners had finished, but near the time when the bulk of the about 27,000 runners were laboring toward the finish line.

 Two bombs hundreds of yards apart went off within seconds of each other on what was also Patriots Day. Dazed and bloodied victims walked around seeking help as officials rushed to their aid, taking them to one of the medical tents that dot any marathon route. Some victims had severed limbs.

 There was no immediate claim of responsibility and officials said there had been no warning to what officials were considering an act of terrorism.

“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,” one federal official said. “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.”

President Obama pledged federal help for the investigation and cautioned people not to jump to conclusions. But he also struck a firm note. read more