An ominous development in Saturday's crash of a Russian plane in Egypt: The airline says pilot error or technical problems could not have caused the crash of Kogalymavia Flight 9268, leaving unspecified "external activity" in the air as the only possible cause, reports the BBC, which notes that an ISIS affiliate is active in the area where the plane went down and that Moscow hasn't ruled out terrorism as a cause. "The only [explanation] for the plane to have been destroyed in mid-air can be specific impact, purely mechanical, physical influence on the aircraft," says airline deputy director Alexander Smirnov. "There is no such combination of failures of systems which could have led to the plane disintegrating in the air." He says that contrary to some reports, the flight did not send out a distress signal or contact air traffic controllers before it broke up midair, reports the AP.
Russian officials, meanwhile, say they've gotten a look at the plane's black boxes and they're in good condition, per the AP. The bodies of around 140 of the 224 victims arrived back in St. Petersburg, the doomed flight's destination, early on Monday, reports the Guardian. A state of official mourning has been declared in the city for what officials say is Russia's deadliest aviation disaster, the Washington Post reports. The Post also reports that major carriers, including KLM and Air France, have decided to avoid flying over the Sinai Peninsula until the cause of the crash is known, though United, the only American carrier to fly over the Sinai, says it does "not see a need" to change its routes immediately. (Read more Russia stories.)