LONDON (AP) - British Prime Minister David Cameron declared Thursday it was "more likely than not" that a bomb brought down a Metrojet flight packed with Russian vacationers - a scenario that Russian and Egyptian officials dismissed as premature speculation.

Cameron said he had grounded all British flights to and from Egypt's Sinai Peninsula because of "intelligence and information" indicating that a bomb was the likely culprit in the crash Saturday that killed all 224 people onboard.

The move stranded thousands of British tourists at the Red Sea resort of Sharm el-Sheikh. Cameron said he had "every sympathy" with the Egyptians, who rely heavily on tourism, but had to "put the safety of British people first."

The Islamic State militant group has claimed responsibility for bringing down the plane, a claim dismissed as not credible by Russian and Egyptian officials.