(CNN) Several senior administration officials in the intelligence, military and national security community told CNN the United States is almost positive a Russian passenger jet was brought down by a bomb.

How convinced are they?

One official said "it's 99.9% certain."

Another official told CNN on Saturday: "We believe it was likely brought down by a bomb."

Russia-bound Metrojet Flight 9268 crashed in Egypt's Sinai Peninsula last weekend, killing all 224 people aboard.

The evidence that it might have been a bomb centers to a large extent on British and U.S. intercepts of chatter after the crash from the ISIS affiliate in Sinai to ISIS operatives in Syria around Raqqa.

U.S. and British intelligence have been analyzing the specific language in the chatter to determine to what extent the operatives were talking about the type of bomb and detonator used, and whether that language was a true representation of what happened, one official told CNN.

Several officials said it's the specificity of the chatter that has directly contributed to the U.S. and British view that a bomb likely was used.

Egypt considering all possibilities

Egyptian officials gave the impression Saturday they are not ready to say there was a bombing.

A noise was heard in the final second of the cockpit voice recording on Metrojet Flight 9268 as it ascended on autopilot before apparently breaking up about 23 minutes after takeoff, the head of Egypt's investigation said Saturday.

No conclusion as to what brought down the flight has been reached, Ayman al-Muqaddam told reporters.

"All the scenarios are out on the table," he said. "We don't know what happened exactly."

In-flight breakup

European investigators who analyzed the two flight recorders are saying the crash is not an accident, CNN affiliate France 2 reported Friday.

Muqaddam said Egyptian authorities have not been provided any information or evidence tied to reports suggesting that a bomb took down the flight. He urged the sources of the reports to pass along related evidence to Egyptian investigators.

Muqaddam did not describe the noise investigators picked up from the cockpit voice recorder when the flight disintegrated midair while traveling at 281 knots (323 mph) at about 30,000 feet and climbing.

"A spectral analysis will be carried out by specialized labs in order to identify the nature of this noise," he said.

The investigation includes experts from Egypt, Russia, France, Germany and Ireland. In recent days the probe has been hampered by bad weather, Muqaddam said.

Debris from the plane was scattered over an area more than 13 kilometers long, suggesting an in-flight breakup, according to Muqaddam.

"Maybe it's a lithium battery, maybe it's an explosion, maybe it's ... a mechanical issue," he said the possible cause of the crash.

Egyptian Foreign Minister Sameh Shoukry said the international community had not heeded Egypt's calls to deal seriously with terrorism.

Other countries "did not show a level of cooperation and direct targeting of these organizations that we hoped for," Shoukry said. "I can say these calls were not heeded by many of the parties who are now working to protect the interests of their citizens."

While couched as a complaint, the statement appeared to mark a significant reversal for Egypt, where officials, perhaps concerned about the fate of the tourist industry, had spent a week rejecting the idea that the Russian plane fell victim to terrorism.

Homeland Security Secretary Jeh Johnson told CNN's Barbara Starr that officials were taking "precautionary interim steps" to increase security on international flights into the United States during the investigation of the Egypt air disaster.

"ISIL is out there now active in a lot of different areas and, while this investigation is pending and because we have this group claiming responsibility, we believe it's significant to do these things on an interim basis," he said, referring to claims of responsibility by the Sinai branch of the terror group also known as ISIS.

Johnson said authorities are evaluating whether additional measures were necessary.

Egypt's announcement

Russian President Vladimir Putin suspended Russian air traffic with Egypt on Friday until the cause of the crash is determined, the Kremlin said.

The United States and Britain shared their intelligence with Russia before Putin decided to suspend flights, Kremlin spokesman Dmitry Peskov told CNN's Matthew Chance.

Putin spoke with Egyptian President Abdel Fattah el-Sisi about the security situation in Egypt.

"The two leaders agreed to strengthen cooperation between the relevant security authorities in the two countries," el-Sisi's office said.

Russia's resistance

Russia had resisted the theory that a bomb brought down the airliner, but with Friday's indefinite suspension of flights it seemed to be moving toward acceptance of the speculation.

The jet, carrying mostly Russian families returning from Red Sea vacations, was 23 minutes into its flight last Saturday from Sharm el-Sheikh to St. Petersburg when it disappeared from radar over the Sinai Peninsula.

Photos: Russian plane crashes in Egypt Photos: Russian plane crashes in Egypt The militant group ISIS published this image of what it claims is the bomb that brought down Metrojet Flight 9268 on Saturday, October 31. The photograph shows a soft-drink can and two components that appear to be a detonator and a switch. Flight 9268 crashed in Egypt's Sinai Peninsula en route to the Russian city of St. Petersburg. All 224 people on board were killed. Hide Caption 1 of 25 Photos: Russian plane crashes in Egypt The wreckage of Flight 9268 is seen in this image provided on Tuesday, November 3. Hide Caption 2 of 25 Photos: Russian plane crashes in Egypt People visit a makeshift memorial at the airport in St. Petersburg on November 3. Hide Caption 3 of 25 Photos: Russian plane crashes in Egypt Trucks in St. Petersburg carry victims' bodies on Monday, November 2. Hide Caption 4 of 25 Photos: Russian plane crashes in Egypt Russian emergency personnel collect personal belongings of victims at the crash site in Hassana, Egypt, on November 2. Hide Caption 5 of 25 Photos: Russian plane crashes in Egypt Egyptian military personnel stand near the tail of the jet in Hassana on Sunday, November 1. Hide Caption 6 of 25 Photos: Russian plane crashes in Egypt A piece of the engine sits on the ground at the crash site on November 1. Hide Caption 7 of 25 Photos: Russian plane crashes in Egypt Egyptian army soldiers guard the luggage and other belongings of passengers piled up at the site of the crash on November 1. Hide Caption 8 of 25 Photos: Russian plane crashes in Egypt Debris belonging to the Russian airliner is shown at the site of the crash on November 1. Hide Caption 9 of 25 Photos: Russian plane crashes in Egypt More debris is shown on November 1. The crash site is in a remote area of a region plagued by a violent Islamic insurgency. Hide Caption 10 of 25 Photos: Russian plane crashes in Egypt Debris from the airliner is seen on November 1. Hide Caption 11 of 25 Photos: Russian plane crashes in Egypt Debris at the crash site on November 1. Hide Caption 12 of 25 Photos: Russian plane crashes in Egypt Candles, toys, flowers and portraits are left at Pulkovo International Airport outside St. Petersburg on November 1. Hide Caption 13 of 25 Photos: Russian plane crashes in Egypt People place flowers and messages in front of the Russian Embassy in Cairo on November 1. Hide Caption 14 of 25 Photos: Russian plane crashes in Egypt Egyptian paramedics load the bodies of victims into a military plane at a military air base by the Suez Canal on Saturday, October 31. Hide Caption 15 of 25 Photos: Russian plane crashes in Egypt Egyptian Prime Minister Sherif Ismail, third from right, visits the site of the plane crash with military and government officials on October 31. Hide Caption 16 of 25 Photos: Russian plane crashes in Egypt Ismail, center, and other officials visit the site of the plane crash on October 31. Hide Caption 17 of 25 Photos: Russian plane crashes in Egypt An item of clothing lies at the site where the plane crashed on October 31. Hide Caption 18 of 25 Photos: Russian plane crashes in Egypt The tail of the jet sits in a field on October 31. Hide Caption 19 of 25 Photos: Russian plane crashes in Egypt Villagers watch an ambulance as it drives to unload bodies on October 31. Hide Caption 20 of 25 Photos: Russian plane crashes in Egypt People light candles and leave flowers at the Russian Embassy in Kiev, Ukraine, on October 31. Hide Caption 21 of 25 Photos: Russian plane crashes in Egypt A relative reacts to news at Pulkovo International Airport on October 31. Hide Caption 22 of 25 Photos: Russian plane crashes in Egypt Employees with the Russian Ministry for Emergency Situations wait in Moscow for their flight to Egypt on October 31. Hide Caption 23 of 25 Photos: Russian plane crashes in Egypt Journalists and spectators wait for ambulances to arrive at the Zeinhom morgue in Cairo on October 31. Hide Caption 24 of 25 Photos: Russian plane crashes in Egypt An Egyptian soldier prays as emergency workers prepare to unload bodies of victims at a military airport north of Suez, Egypt, on October 31. Hide Caption 25 of 25

A U.S. satellite detected a heat flash over Sinai. The plane broke apart and fell 30,000 feet. All aboard died.

Russia's about-face buttressed a theory about the cause of the crash. As investigators pick through the rubble of the Russian airliner, and as Western officials sift through their own intelligence reports, some suspect Flight 9268 was brought down by a bomb planted in its hold.

And some believe think the bomb may have been smuggled on board in the Egyptian resort of Sharm el-Sheikh, from which the flight departed.

Since Friday, 1,200 Russian citizens have been evacuated from Egypt on 6 planes, Russian state broadcaster Russia 24 reported, quoting Oleg Safonov, the chief of Russia's Federal Agency for Tourism Oleg Safonov. The channel reported that the Egyptian military checked the passengers before they boarded the planes.

About 80,000 Russian tourists remain in Egypt, with 79,000 of them in Hurghada and Sharm el-Sheikh, he said. Hurghada, like Sharm el-Sheikh, is a Red Sea tourist city.

And UK officials were "urgently" working with Egyptian authorities on "permanent measures that will allow British tourists to come back to Sharm el-Sheikh as soon as possible," the British Embassy in Cairo said Saturday. The embassy statement said "Britain is not evacuating its tourists early from their holidays."

Bomb theory

The bombing theory emerged Wednesday, when Britain suspended flights from Sharm el-Sheikh to the United Kingdom because of security fears.

It gained currency when it was expressed publicly by British Prime Minister David Cameron and U.S. President Barack Obama, though neither called it a certainly.

Talks between the United States, Egypt and Russia could result in the FBI providing some experts, particularly bomb technicians, to assist in the investigation, according to a U.S. official.