The Governor of Massachusetts says that only two explosive devices were found in Boston where 3 people died and more than 150 others were injured in bomb blasts last night. It contradicts earlier reports that a number of other unexploded devices were recovered.
The FBI are interviewing a number of eyewitnesses as they investigate what the White House has described as an "act of terrorism".
Politicians from all across the spectrum here have paid tribute to those affected by events yesterday. 108 Irish citizens - 50 of whom were listed as residing in Ireland - had registered to take part in the event. All of those have now been accounted.
Taoiseach Enda Kenny has described the attack as an "act of insanity".
"This is an act of insanity. When so many people enjoyed the preparation for that wonderful race and the occasion itself" he said.
"We sympathise with the people of Boston in a city that is so Irish - this is a tragedy".
"I do hope that the authorities - from Federal level down to local level - will get to the root of this, and bring those perpetrators of this particular crime to justice in the shortest possible time" he added.
US President Barack Obama has pledged to bring the individual or group behind the attack to justice.
Speaking from the White House last night he said "I've also spoken with Governor Patrick and Mayor Menino, and made it clear that they have every single federal resource necessary to care for the victims and counsel the families".
"Above all, I made clear to them that all Americans stand with the people of Boston" he added.
Bureau spokesman Rick Des Lauriers has appealed for co-operation.
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Meanwhile online security experts are warning against the danger of internet scams in the wake of the Boston bombing.
Scammers use social networking sites to direct people to their websites by piggy-backing on the news story.
Shortly after the story broke an unverified Twitter account was already spotted asking for re-tweets claiming that they will donate US$1 for each.
Experts advise twitter users to avoid unknown or shortened links - as they could lead you to infected websites.
The FBI is taking charge in the criminal investigation. An official has said 'it is a potential terrorist investigation'.
