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Homeland Security Secretary Jeh Johnson on Friday ordered new security measures aimed at some Middle Eastern airports "out of an abundance of caution" after the suspicious crash of a Russian airliner that President Obama suggested could have been caused by a bomb.

A White House spokesman on Friday wouldn't elaborate on what prompted Obama's statement on Thursday that a bomb may have caused the incident, beyond noting that he based it on "what the United States has learned in the last few days" about the investigation into Saturday's crash of the Metrojet flight after it departed Egypt's Sharm el Sheikh airport.

Spokesman Josh Earnest said that he has to "protect sources and methods" and, therefore, couldn't offer more details about what exactly U.S. officials now know about the crash.

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