U.S. and U.K. officials are now increasingly focused on the idea that a bomb brought down the Russian jetliner that crashed in Egypt.
According to Prime Minister David Cameron, the cause of the downing of a Metrojet Airbus 321 bound for Russia was "more likely than not a terrorist attack."
ISIS is suspected of paying a baggage handler or airline official -- to get a bomb onto the Metrojet airliner, but other possibilities haven’t been ruled out, the officials said.
ISIS had already claimed they downed the plane in retaliation for Russia fighting the group in Syria.
As a cautionary measure, the U.K. issued an advisory against all but essential travel to or from Egypt’s Sharm el-Sheikh airport, where the doomed plane took off Saturday, and Irish regulators ordered Ireland-based airlines not to fly to the Red Sea resort or the the Sinai Peninsula until further notice.
“The reaction of Russia and the international community will be harsh” if a bomb did destroy the plane, though the investigation should be allowed to conclude its work, Franz Klintsevich, deputy head of the defense committee of the Federation Council, Russia’s upper house of parliament, said by phone Thursday. “Security measures will be strengthened even further.”