Police say they are questioning an individual over "suspicious envelopes". Two letters - one addressed to Barack Obama and the other addressed to Senator Roger Wicker - have been found to contain the poison ricin.
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The Queen opened this year's Commonwealth summit with the message that "a nation's size is no measure of the moral strength of its people".
French President Francois Hollande today led a memorial service to the 130 victims of the Paris attacks in the city.
Cameron announces Commonwealth nations intention to set up specialist unit to target extremist "scourge" fuelling international terrorism.