Local media is reporting two suspicious packages have been identified near to the finish line of the Boston Marathon, prompting evacuations.
A memorial service has been taking place to mark the first anniversary of the bombings.
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Cooler and fresher across the UK over the next few days.
The prime minister was shouted at as she left the scene of the tragedy in which at least 79 people died.
Father-of-six Makram Ali, 51, was already receiving medical treatment as the attack unfolded. He died from multiple injuries, police say.