Britain attacks: Lack of pattern puts officials on edge: The randomness of the three terrorist attacks in Britain since March 22 puts officials around the world on edge, making it difficult to anticipate a next strike.
In the United States, New York Mayor Bill de Blasio said Sunday that his city was on high alert, with critical response units in "particularly prominent" locations.
The Islamic State, also known as ISIS, claimed responsibility for Saturday night's attack in London that left seven people dead and wounded dozens. ISIS also claimed responsibility for the previous two British attacks.
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