MOSCOW -- As tens of thousands of Russian tourists hastily leave Egypt's economically vital seaside resorts, a top Kremlin official issued an ominous warning Tuesday: They're not coming back anytime soon.

Russia last week suspended all passenger flights to Egypt in the wake of the Oct. 31 airliner crash in the Sinai peninsula that killed all 224 people on board, almost all of them Russians. Moscow said the ban was necessary because of concerns about security at Egypt's airports.

Russian officials say they haven't determined whether a bomb brought down the plane as it flew from Sharm al-Sheikh toward St. Petersburg. But the flight ban and unspecified concerns about airport security suggest Russia takes the prospect exceptionally seriously.

On Tuesday, President Vladimir Putin's chief of staff, Sergei Ivanov, said the flight ban will last for at least several months. Speaking on a visit to Finland, he said it would be impossible to radically revise Egypt's security system in a short time, according to Russian news reports.

Ivanov said Egypt needs to improve its security regime not only in Sharm el-Sheikh, but also in airports in Cairo and the Red Sea resort of Hurghada.

Asked how long the Russian flight ban would last, Ivanov said: "I think for several months, as a minimum."

It's unclear whether Egypt's tourist resorts, shops and restaurants can hold on that long, especially since the travel ban hits in the lucrative winter high season. Russians have accounted for about a third of all Egypt's tourists in recent years.

Other airliners from Britain and Western Europe were also bringing their nationals home, after several countries and airlines suspended flights to Egypt amid suspicions that a terror attack could be the cause of the crash of the Airbus A321-200 operated by Metrojet.

U.S. and British officials have cited intelligence reports indicating that the plane was brought down by a bomb on board. Russia and Egypt said the statements were premature pending results of the official crash probe.

Security officials at Sharm el-Sheikh airport told The Associated Press there have long been security gaps there, including a key baggage scanning device that often is not functioning and lax searches at an entry gate for food and fuel for the planes.

The head of Cairo's international airport, Maj. Gen. Ahmed Genina, said officials from Russia, the Netherlands, Italy, the United Arab Emirates and Qatar were examining the scanning of passengers, cargo and baggage at the airport Tuesday. Security guards and caterers were also being inspected.

The Russian ban has badly struck Egypt's vital tourist sector, which represents 11 per cent of its economy and almost 20 per cent of crucial foreign currency revenues. The industry had been making a gradual recovery after years of political upheaval since the 2011 popular uprising that deposed longtime autocrat Hosni Mubarak.

Egypt is one of the most popular destinations for Russians, especially in the winter when the sun and clear seas lure them away from grey, frigid weather.

Roughly 3 million Russian tourists came to Egypt in 2014, nearly a third of all visitors, with most heading to the resorts in the southern Sinai Peninsula or its opposite coast, far from the insurgency being fought by Islamic militants against the army further north.

Eastern European visitors, including people from former Soviet satellite states like Ukraine, made up a crucial 45 per cent of all tourist arrivals in June, according to Egyptian government statistics.

Within hours of the Metrojet crash, a faction of the Islamic State militant group claimed to have downed the plane in retaliation for Russian airstrikes that began a month earlier against militants in Syria, a claim that was initially dismissed by both Russia and Egypt.

Ivanov said a terror attack is one of several possible explanations, adding that the probe into the crash will involve complex chemical and other tests and will likely drag into next year. "We halted the flights to Egypt without knowing the definitive version, we did it preventively, out of caution," Ivanov said.

He added that Russia's air campaign in Syria will continue regardless of the outcome. "The course of the operation against terrorists in Syria doesn't depend on the investigation into the crash," Ivanov said.

Commenting on media reports that Moscow was also mulling suspension of flights to other destinations in the Middle East, Ivanov said Russian intelligence agencies have made no such decision, but added that Moscow was monitoring the general security situation and airport security in other countries in the region.

Since the Russian suspension of flights to Egypt was announced Friday, dozens of airliners have been bringing Russian tourists back home, carrying only cabin baggage, while Russian cargo planes were hauling the rest of their luggage.

About 40,000 Russian tourists have been flown back since Friday, about half the number in Egypt when flights were suspended, according to a Russian government estimate.