MOSCOW -- President Barack Obama and other senior Western officials said Thursday that a bomb may have caused a Russian passenger jet to crash in Egypt last weekend, redoubling speculation about a terrorist attack despite heated protests from the governments of both Russia and Egypt.

In a radio interview with Seattle-based KIRO Radio, Obama said, "I think there is a possibility that there was a bomb on board and we're taking that very seriously."

"We're going to spend a lot of time just making sure our own investigators and own intelligence community find out what's going on before we make any definitive pronouncements. But it's certainly possible that there was a bomb on board," he said.

U.S. intelligence officials and key legislators echoed the president's remarks but cautioned that the cause has not been confirmed. "There are certainly indications that it may have been an explosion, may have been a terrorist bomb on the aircraft, but it remains a possibility that it was a structural failure in the aircraft," said Rep. Adam B. Schiff of California, the ranking Democrat on the House Intelligence Committee, speaking on MSNBC Thursday. "And the intelligence community is not really at a point where it can confirm either hypothesis."

Russia and Egypt have called for patience while an official investigation that also includes Germany, France and Ireland reviews the crash over the next several months. But many European governments have already taken steps to protect themselves.

One day after halting all flights to and from the Egyptian resort town of Sharm el-Sheikh, a spokesman for British Prime Minister David Cameron on Thursday announced that inbound flights would resume to ferry thousands of stranded vacationers back to Britain under strict new security measures.

Under the new rules, passengers are permitted only hand luggage.

The new precautions reflect assertions by Western officials that lax security at the Sharm el-Sheikh airport may have allowed terrorists to smuggle a bomb aboard the Airbus 320-200, killing 217 passengers and seven crew members Saturday.

The head of Russia's aviation agency, Alexander Neradko, said it could be "at least several months" before an official finding is made on what caused the plane to break apart in midflight.

But on Thursday, Cameron, citing intelligence reports, said that a bomb "more likely than not" was the cause.

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The statement provoked angry recriminations from Russian and Egyptian officials. Egypt is battling an Islamist insurgency in the Sinai Peninsula, and the bombing would undercut President Abdel-Fatah el-Sissi's claims that the situation is under control.

Meanwhile, the Islamic State's affiliate in Egypt has repeatedly claimed responsibility for the crash, which it called revenge for Russia's intervention in the war in Syria.

Egypt's Civil Aviation Ministry, meanwhile, stated that the British theory of a bomb smuggled aboard "is not based on facts" and that all of the country's airports apply international security standards.

Nearly 40 flights from seven countries, including Russia, were to land Thursday in Sharm el-Sheikh, but other carriers joined the list of those suspending flights. U.S.-based carriers do not fly to the city.