Egypt insisted on Thursday its airports were secured to international standards, despite growing concerns that its screening procedures may be flawed and that Islamist militants may have downed a Russian plane by smuggling a bomb on board.
Earlier Britain said a bomb planted by an Islamic State affiliate active in the Sinai Peninsula may have caused the jet to crash on Saturday, killing all 224 people on board. It halted flights to Sharm al-Sheikh - from where the doomed plane flew - pending security checks, a move quickly followed by Ireland, Germany and the Netherlands.
Egyptian and Russian officials have said it is too early to conclude a blast had brought down the plane.
"All Egyptian airports apply international standards in airport security measures," civil aviation minister Hossam Kamal said in a statement, adding that the investigation was ongoing.
But Egypt also promoted the airport chief at Sharm al-Sheikh, a resort popular with British, Russian and other European holidaymakers seeking winter sun, to deputy head of operations at the national airport operator.
The timing of that move, along with a steady string of security breaches, have stirred doubts about airport safety around Egypt.
A day after Islamist militants claimed responsibility for downing the Russian plane, two men cleared the fence at another Red Sea airport, in the resort of Hurghada, and were arrested before they reached the runway, a judicial source said.
The source said the youths were criminals planning a robbery but some local media had earlier reported that the men had reached an airplane bound for Spain in the hope of stowing away under the wheels to start new lives in Europe.
"How did two youths who were not travelling, without passports, without visas, with nothing, get to the airplane?" asked Amr Abdelhamid, presenter of a current affairs program on private television channel TEN.
In another incident in April, a donkey was found wandering around the carpark at Cairo airport and was captured on a video that went viral, with Egyptians tweeting sarcastic comments hashtagged in Arabic "how did the donkey enter the airport?"
"He thought and thought and exploited a security loophole," one person tweeted, mocking what they said was the official explanation for the breach, also carried in newspapers.
Though Egyptians made light of these incidents with their typically caustic humor, they underscored the widely-held view that standards are low and the potential for corruption high in poorly-paid public sector jobs including travel security.
Aside from the loss of lives, at stake are the fate of Egypt's tourist industry, a vital source of hard currency in a struggling economy, and the credibility of President Abdel Fattah al-Sisi's claims to have brought under control the militants fighting to topple his government.
Egypt's tourist industry took years to recover after militant Islamist gunmen killed 58 tourists and four Egyptians at an archaeological site near Luxor in 1997.
At Sharm al-Sheikh airport, security appeared to have been tightened on Thursday, with security forces patrolling the terminals and not allowing drivers, tour agents or others to loiter while awaiting tourist arrivals, a witness said.
Britain said it was working with airlines and Egyptian authorities to put in place more security and screening measures to allow thousands of stranded British tourists to get home.
Foreign Secretary Philip Hammond said short-term measures would include more levels of baggage screening and searching in order to double-check everything going onto planes.
One particular issue raised by security officials appears to revolve around baggage handlers and other staff.
One U.S. government source said security at Sharm al-Sheikh airport was porous and that militants could have infiltrated or bribed their way into secure zones. Another noted that no major U.S. carrier flies into or out of Sharm, suggesting that inadequate security was one reason for this.
Noting that London was hosting Sisi on Thursday, Bruce Riedel, a former CIA expert on the region, said: "British intelligence is very thorough. The prime minister's office knew suspending Sinai flights on the eve of Sisi's visit would be a major embarrassment so I'm confident the intelligence was pretty strong pointing to a bomb."
"Security at other airports in Egypt including Cairo could well be compromised, given the large number of angry young Egyptians who believe their revolution was stolen."
Meanwhile, U.S. President Barack Obama said on Thursday there was a "possibility" that the crash was caused by a bomb on board the airliner.
"I think there's a possibility that there was a bomb on board. And we're taking that very seriously," Obama said in an interview with KIRO/CBS News Radio that was quoted on CNN.
"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.
Egypt has struggled to lure back tourists since the 2011 uprising that ended Hosni Mubarak's 30-year rule ushered in a period of political instability.
Mohamed Mursi of the Muslim Brotherhood won Egypt's presidential election after the uprising, but Sisi - then army chief - removed him from power in 2013 after mass protests. Sisi then banned the Brotherhood, jailed thousands of its members and cracked down on an increasingly violent Sinai insurgency.
The Brotherhood says it is not linked to Sinai-based militants who have claimed responsibility for the plane incident. The government treats both as terrorists and a downed jet would raise questions about the effectiveness of its policy.
Travelers departing from Egyptian airports are required to put their luggage through scanners before check-in and again before boarding.
Additional security measures are in place for flights to particular destinations, notably London, at the request of those authorities, airport security sources said.
These may involve, for instance, passengers removing their shoes for inspection, the sources said.
Egyptian intelligence and security agencies also carry out background checks on anyone seeking employment at any airport.
Egypt must follow regulations set out by the International Civil Aviation Organization (ICAO), the aviation safety arm of the United Nations regarding passengers, staff and baggage.
European Union airport security levels are stricter than those of ICAO and Britain in turn has its own special measures in place, which takes its security a notch higher still.
Speaking at a news conference in London, Sisi said Britain had approached his country 10 months ago with a view to reviewing airport security and Egypt had complied.
Security sources said Britain had provided advanced explosives detection technology for use at Sharm al-Sheikh.
One expert said more covert testing was needed to make sure standards were upheld in Egypt and more awareness was needed that threats were not limited to passengers and their bags.
"You can have the best procedures in the world, but is everyone following them?" Matthew Finn, managing director of independent aviation security consultants Augmentiq, said.
One issue, Finn said, is that airport staff often aren't paid much money and can lack the right skills as a result.
British passengers who have traveled in the past through Sharm airport took to Twitter on Thursday to describe lax security, such as staff being more interested in their phones than checking bags. But some said they felt security was fine.
Despite some cancellations, flights continue to arrive at Sharm, said Civil Aviation Minister Kamal, including 23 from Russia on Thursday.
While the police presence was heavy in Naama Bay, the main strip of hotels and restaurants in Sharm al-Sheikh, shops were open on Thursday night and tourists appeared to be relaxed.