Maxim Grigoriev/Russian Ministry for Emergency Situations via AP
Egyptian Military on cars approach a plane's tail at the wreckage of a passenger jet bound for St. Petersburg in Russia that crashed in Hassana, Egypt, on Sunday, Nov. 1, 2015. The Russian cargo plane on Monday brought the first bodies of Russian victims killed in a plane crash in Egypt home to St. Petersburg.
The Sharm el-Sheikh airport, from which the plane left on its way to St. Petersburg, is beefing up security in response to the possible attack.
But before now, security might have been lax enough to create an opening for terrorists looking for an opportunity to strike.
Egypt is "probably the best place to get a Russian airliner," Michael Kofman, an expert on security and Russia and a public-policy fellow at the Wilson Center, told Business Insider. "If you look at where Russian tourists go, where else are you going to get a soft civilian target like that?"
Egypt is a popular tourist destination for Russians, and it's likely easier to carry out a terrorist plot there than in some other countries that see a lot of Russian visitors.
"Turks are very geared up for terrorism. Egyptians are not," Kofman said. "It's not that hard of a reach for somebody with a fairly sophisticated terrorist network or intelligence operation."
Rep. Adam Schiff (D-California), the ranking member of the House Intelligence Committee, also said it's possible that ISIS (also known as the Islamic State or ISIL) would have the capability to carry out such an attack.
He told MSNBC on Thursday that it "doesn't require a lot of sophistication, unfortunately, to get a bomb on an aircraft."
"You have to defeat the airport security. We have, obviously, much better airport security here at home, but even our airport security is far from infallible," Schiff said.
He added: "If you have someone on the inside at the airport that can help you smuggle an explosive onto an aircraft, that obviously doesn't require a great deal of sophistication. It just requires having one person in the right or - in this case - the wrong place."
Schiff also noted that ISIS's affiliate in Egypt's Sinai peninsula - where Sharm el-Sheikh is located - is becoming larger and more sophisticated. ISIS's Egypt branch claimed responsibility for the plane crash, but ISIS's central leadership has so far remained silent on the supposed attack.
UK Prime Minister David Cameron said Thursday that a bomb "more likely than not" brought down the plane. US President Barack Obama on Thursday said the US was taking "very seriously" the possibility a bomb caused the crash.
REUTERS/Kim Philipp Piskol
The Metrojet's Airbus A-321 with registration number EI-ETJ that crashed in Egypt's Sinai peninsula, is seen in this picture taken in Antalya, Turkey September 17, 2015.
Michael Pregent, a military analyst and former US Army intelligence officer, echoed Schiff's concerns about Sharm el-Sheikh's airport security.
"I spent a year in Sinai in 2000 and flew out of that airport many times," Pregent told Business Insider. "No plane ever left on time and there was never any sense of urgency, and you could see that translate to the security. I think it's very likely that they were able to get somebody to put a bomb on the aircraft."
US intelligence officials reportedly consider terrorism the "leading theory" in what happened to the plane that was carrying 224 people and broke up in midair about 20 minutes into the flight, according to CBS News. The investigation is ongoing and experts will look at the wreckage for signs of an explosion caused by a bomb.
Egypt's civil aviation minister said its airport security is up to international standards, according to CBS.
But the UK reportedly raised concerns about security at Sharm el-Sheikh's airport last year, according to The Guardian. One airport employee told the newspaper that UK officials complained that airport staff wasn't "checking people enough." Concerns reportedly included luggage screening.
AP Photo/Dmitry Lovetsky
People light candles during a day of national mourning for the plane crash victims at Dvortsovaya (Palace) Square in St. Petersburg, Russia, on Sunday, Nov. 1, 2015.
Egypt is now reportedly investigating airport employees.
ABC News had a fuller, detailed look at the new security procedures at the airport in the wake of the incident:
New security measures include searching all staffers, including high-ranking airport officials, at the airport by X-ray scanners. They are also being asked to take off their shoes.
The number of metal detectors each person walks through will be increased from two to four and old detectors are being replaced with new ones. Authorities have been asked to double the number of sniffing dogs and to spread them more widely, including to the plane catering department. The authorities asked for sophisticated detectors and more advanced ones.
As for luggage, police will open and search any suspicious bags; all liquids will now be banned except for medicine.
ISIS has used Russian airstrikes in Syria as the supposed motive for the attack it says it carried out. For its part, a Russian Foreign Ministry spokeswoman seemed to indicate frustration with the British government's intelligence sharing.
"Frankly speaking, it is genuinely shocking to think that the British government has some kind of information that could cast light on what happened in the skies above Egypt. If such information exists, and judging by what the foreign secretary has said it does, no one has passed it to the Russian side," said Maria Zakharova, the spokeswoman, according to The Guardian.