Boston police: 3rd explosion at library

JIMMY GOLEN
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Medical workers wheel the injured across the finish line during the 2013 Boston Marathon following an explosion in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts. (AP Photo/Charles Krupa)

BOSTON (AP) — Boston police say there's been a third explosion in the city, following two blasts near the finish line of the Boston Marathon that killed two people and injured many others.

Police Commissioner Edward Davis says authorities aren't certain that the explosion that occurred more than an hour later at the JFK Library was related to the other blasts, but they're treating it as if it was.

Davis says there are no injuries stemming from the third explosion. The total numbers of casualties from the other blasts isn't known.

Davis urged people to stay indoors and not congregate in large groups.

Police say they received no information before the explosions to indicate they were coming.