Bill Iffrig, 78, lies on the ground as police officers react to a second explosion at the finish line of the Boston Marathon
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FBI probes Boston Marathon 'terror' blasts

An investigation is under way after two explosions near the finishing line of the Boston Marathon left three people dead and more than 170 injured.

The FBI has taken over co-ordination of what it described as a "potential terrorist inquiry".

Security has been stepped up in a number of cities across the US, including New York and Washington.

Ian Pannell reports from Boston.

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