A third potential bomb explosion incident at JFK Library in Boston has been confirmed as entirely unrelated to the Boston Marathon bombings on Monday afternoon.

The incident was previously highlighted by Boston police as being suspicious and in the immediate aftermath of the bombings authorities were investigating that 3rd incident as connected.

However, it has now been confirmed that the JFK Library incident was unrelated and was fire-related and mechanical.

Earlier, just before 3 p.m. two large bomb explosions were seen at the Boston Marathon route near the finish line, killing at least 2 and injuring at least 100 others, including as many as 6 in critical condition.

Reports just before 6 p.m. ET stated that the Boston Marathon bombings were now being officially treated as a terrorist attack, according to the FBI.

The White House also confirmed that President Barack Obama would address the nation briefly at about 6.10 p.m. ET.

The devastating scenes at the Boston Marathon have shown injured people being carried away from the scene of the explosions, which took place near the finish line of the marathon route.

Witnesses reported that two loud bangs were heard near the finish line, and video footage can be seen at the moment of the explosions with a big fireball seen coming from one of the buildings to the side of the road.

Other early reports are claiming more injuries are expected to be reported. Some reports have claimed that some bloodied victims were taken to a medical tent for treatment, and many others have been taken to hospital. Some of those being treated in hospital are said to have suffered critical injuries and have been taken immediately to the emergency room.

Smoke could be seen coming from the Marathon Sports store and marathon officials were seen pulling at some metal railings that were twisted and piled on the ground, seemingly to free some people under them. Other eye witnesses reported a bloody scene, with some victims being very seriously injured near the scenes of the explosions.

Police are being deployed to major landmarks in other large cities across the United States, including New York City, as fears of a possible terrorist attack emerge.

Here is video footage in the aftermath of the bombings: