Suspicious letter addressed to US President Obama has tested positive for the deadly poison ricin, as did a letter to a Republican Senator.
The FBI assessment is that there are no links between the poison letters to Obama and Senator Roger Wicker and the bombs at The Boston Marathon.
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Six people have been injured and a man has been arrested after an alleged noxious substance attack in east London.
The US first lady travelled without her husband to support the Invictus Games, which were founded by the Prince in 2014.
The Pentagon sent a group of military planes just off the state's coast in a show of force.