Increased security measures are activated by the US and other countries at government, public buildings, and sports venues. On Monday April 15, 2013 two bombs exploded in the crowded streets at the Boston marathon in the United States.
The United States and other countries increase security in response to deadly bombings in Boston
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Federal Bureau of Investigation (FBI) agents arrive at the scene after explosions near the finish line of the Boston Marathon in Boston, Massachusetts April 15, 2013.
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Backdropped by Buckingham Palace, Queen's Life Guards and police offcers ride down the Mall in London where the finish area of the forthcoming London Marathon.
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Members of the U.S. Army National Guard Joint Task Force Empire Shield patrol Grand Central Terminal in New York, April 16, 2013.
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Boston police officers keep a perimeter secure in Boston's Copley Square.