Here's what we know about the deadly Russian plane crash that killed all 224 people on board Saturday, Oct. 31. (Monica Akhtar/The Washington Post)

President 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 while a bomb may have brought down the Russian plane, that 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 (Calif.), the ranking Democrat on the House Intelligence Committee, speaking on MSNBC on Thursday. “And the intelligence community is not really at a point where it can confirm either hypothesis.”

Schiff also described as “very forward-leaning” remarks by British Foreign Secretary Philip Hammond that a bomb is a “significant possibility.”

“I can only tell you our perspective here in the United States, which is we aren’t ready to confirm anything,” Schiff said.

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 Britain halted all flights to and from the Egyptian resort town of Sharm el-Sheikh, a spokesman for 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. Hold luggage will not be transported aboard the passenger planes.

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. Other theories for the crash include ­pilot error or a technical malfunction.

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 flight, scattering debris over seven square miles of desert.

But Cameron on Thursday, citing intelligence reports, said that a bomb “more likely than not” was the cause of last weekend’s crash.

The statement provoked angry recriminations from Russian and Egyptian officials.

Egypt is battling an Islamist insurgency in the Sinai Peninsula, and a bombing would undercut President Abdel Fatah al-Sissi’s claims that the situation is under control.

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

Russian Foreign Ministry spokeswoman Maria Zakharova said it would be “shocking” if Britain had information that could “shed some light on what happened in the skies over Egypt.”

“If this information exists — and it seems to exist judging by the fact that the foreign secretary made it public — nobody has passed it on to Russia,” Zakharova said.

Egypt’s Civil Aviation Ministry, meanwhile, said in a statement that the British theory of a bomb having been smuggled aboard the plane “is not based on facts” and that all of the country’s airports apply international security standards.

“The investigation team does not have any evidence or data confirming this hypothesis,” Civil Aviation Minister Hossam Kamal said, according to the statement.

Cameron received Sissi at 10 Downing Street on Thursday. Despite expectations that the meeting would be tense, the two men played down any signs of tension in public.

Earlier this week, Sissi told the BBC in an interview that speculations about terrorism were designed “to damage the stability and security of Egypt and the image of Egypt.”

But at a post-meeting news conference Thursday, Cameron said the two men were “committed to work together” to address security challenges at the airport.

Sissi said that British officials had first raised concerns about Egyptian airport security 10 months ago and that Britain and Egypt had since been working cooperatively on the issue. He said the two governments were hoping to “restore the movement of British tourists” as quickly as possible.

Dutch airline KLM said it would resume flights from Sharm el-Sheikh to Amsterdam on Friday, also with no hold luggage.

Nearly 40 flights from seven countries, including Russia, were due to land Thursday in Sharm el-Sheikh.

But other carriers joined the list of those suspending flights to the Sinai city. Among them was Lufthansa, which said its subsidiary airlines — Edelweiss and Eurowings — were halting service to the Red Sea resort. U.S.-based carriers do not fly to the city.

On Wednesday, the Islamic State in an audio clip appeared to taunt Russian and Egyptian officials who have sought to play down suggestions that terrorism was to blame.

“Search the wreckage of the plane and bring forth your black box and analyze it. Show us your expertise, and prove that we did not cause the plane to crash,” the group said. “We shall reveal in the coming days the mechanics of bringing down the plane, at the time we want and through the method we deem best.”

Witte reported from London. Erin Cunningham and Heba Habib in Cairo, Ashley Halsey III and Adam Goldman in Washington and Karla Adam in London contributed to this report.