The Federal Aviation Administration closed airspace over a 7-mile-wide (11 km) stretch of the northwest Boston area on Friday to provide a "safe environment for law-enforcement activities" as police searched for a second Boston Marathon bomb suspect.
The restriction, which echoes similar measures imposed after Monday's bombing, applies to all aircraft flying below 3,000 feet (914 metres), according to an FAA bulletin.
There were no immediate reports of restrictions at Boston's Logan airport.
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