London, Cairo: US President Barack Obama raised the possibility that a bomb brought down a Russian plane that crashed over Egypt's Sinai Peninsula, undermining efforts by Cairo and Moscow to downplay the suggestion of an attack.
With concerns over security mounting, a number of European airlines readied to bring home thousands of tourists from the Red Sea resort of Sharm Al-Shaikh, where the plane took off last Saturday.
The Daesh (Islamic State) jihadist group has claimed responsibility for the disaster, in which the Saint Petersburg-bound jet crashed minutes after taking off, killing all 224 mainly Russian tourists on board.
“I think there is a possibility that there was a bomb on board and we are taking that very seriously,” Obama told a US radio station, while emphasising it was too early to say for sure.
In London, where David Cameron was hosting Egyptian President Abdel Fattah Al-Sissi, the British premier told reporters it was “more likely than not that it was a terrorist bomb” that caused the crash.
Intercepts
And The Times newspaper reported on Friday that electronic communications intercepted by British and American spies suggested a bomb may have been carried onto the plane.
“The tone and content of the messages convinced analysts that a bomb had been carried on board by a passenger or a member of the airport ground staff,” the newspaper reported, without giving a source.
But Egypt's civil aviation minister Hossam Kamal said there was "as yet no evidence or data confirming the theory" of an attack and the Kremlin has dismissed the notion as "speculation".
Russian President Vladimir Putin, who authorised strikes against fighters including Daesh militants in Syria, said assessments of the crash should be based on the “ongoing official investigation”, according to the Kremlin.
Al Sissi sought to use his trip to London Thursday to allay fears over the safety of tourists in his home country after several nations suspended flights to and from Sharm Al-Shaikh - leaving holidaymakers stranded while officials assessed security at the airport.
There is no global or European blanket ban and some flights have continued from the airport, but France and Belgium have warned citizens against travelling to Sharm Al-Shaikh and Britain has advised against all but essential travel by air to or from the resort.
Outbound flights from Britain to Sharm Al-Shaikh remain suspended but the British government authorised flights to resume from the resort on Friday to bring home an estimated 20,000 British tourists - but passengers will only be allowed to carry hand luggage.
"The government has decided, in consultation with the airlines, that flights from Sharm to the UK will resume tomorrow," a spokeswoman for Cameron said.
"The additional security measures will include permitting passengers to carry hand baggage only and transporting hold luggage separately."
Flights cancelled
Belgian airline Jetair announced similar measures, while British airlines easyJet and Monarch said they would lay on extra flights to get customers home.
Joining a string of airlines in avoiding Sharm Al-Shaikh, the Lufthansa Group announced its subsidiary Eurowings would halt flights between Germany and the Red Sea resort, while Turkish Airlines also cancelled two flights.
Russia on Thursday began burying the first victims of the crash, with several hundred people gathering in Veliky Novgorod, south of Saint Petersburg, to mourn 60-year-old Nina Lushchenko.
Flight KGL9268 was flying at altitude of 30,000 feet (9,150 metres) when it lost contact with authorities, 23 minutes after take-off from Sharm el-Sheikh to Russia's second city.
Experts say the fact that debris and bodies were strewn over a wide area indicates the aircraft disintegrated in mid-air, meaning the crash was likely caused by either a technical fault or an explosion on board.
Daesh claimed responsibility for the crash on a number of occasions, said Wednesday it would reveal how it had done so at a time of its choosing.
If confirmed, it would be the first time IS, which controls large areas of Syria and Iraq, has attacked a passenger plane. It has the potential to deeply damage Egypt's tourism industry, still struggling to recover from a turbulent few years following the revolution of 2011.
Security dragnet
The Daesh branch in Egypt suspected of bringing down a Russian airliner in eluded a security dragnet by operating in secretive cells inspired by a leader who used to import clothes for a living, Egyptian intelligence officials say.
Western officials are increasingly pointing the finger of blame at Sinai Province, which has focused on killing Egyptian soldiers and police since the military toppled President Mohamed Mursi of the Muslim Brotherhood in 2013 after mass protests.
If solid evidence emerges it attacked the aircraft, that would instantly propel the group to the top of the jihadi ladder, with one of the deadliest attacks since al Qaeda flew planes into the World Trade Center in New York in 2001.
If a bomb knocked Airbus A321 out of the sky, that would challenge Egypt's assertions that it had brought under control militants who have carried out high-profile attacks on senior government officials and Western targets.
Security experts and investigators have said the plane is unlikely to have been struck from the outside and Sinai militants are not believed to have any missiles capable of striking a jet at 30,000 feet.
Sinai Province is partly the product of Egypt's efforts to eliminate militancy, which has threatened the most populous Arab country for decades, according to the intelligence sources.
The three officials, who closely follow the Sinai-based insurgency, say many of its fighters fled to Syria after Mursi was removed and then army chief Abdel Fattah al-Sisi unleashed security forces on Islamists, both moderate and radical.
Sinai Province's leader - a 42-year-old former clothes importer known by his nom de guerre Abu Osama al-Masri - studied at Al-Azhar, a 1,000-year old Egyptian centre for Islamic learning that supports the government, said the officials.
But like others who learned in a centre known for its moderation, he was radicalised and took up arms in Sinai before heading to Syria with about 20 followers when security forces clamped down on Islamists after Mursi's departure, the sources said.
'THEY BECAME EXPERTS' There, he and the other fighters gained experience that would prove useful upon their eventual return to the Sinai, when they were approached by Islamic State and embraced its goal of creating a caliphate across the Muslim world.
It seems they were mesmerised by Islamic State's mysterious Iraqi leader, Abu Bakr al-Baghdadi, said the officials.
Islamic State sent arms and cash by boat from Iraq to neighbouring Libya, where militants have thrived in the chaos that followed the fall of Muammar Gaddafi in 2011, said another intelligence official.
A porous border then enabled Baghdadi's supporters to travel to Sinai, on the other side of Egypt, to deliver the goods to Islamist militant comrades, the officials added.
"Other militants taught them how to evade capture and they learned how to shoot accurately and assemble bombs," said one of the intelligence officials, speaking on condition of anonymity.
"They became experts." Will McCants, director of the Center for Middle East Policy at the Washington-based Brookings Institution, said that not a lot is known about the working relationship between the Islamic State's Sinai affiliate and the movement's central leadership.
But the Egyptian group - like other affiliates - appears to enjoy considerable autonomy.
The state security crackdown launched against the Muslim Brotherhood and other Islamists has gained the Islamic State's Sinai branch significant local support, allowing its fighters to hide and operate among ordinary people, he said.
SECRETIVE During Mursi's time, security officials allege, militants from al Qaeda, including some who had travelled from as far away as Afghanistan, had a free hand in Sinai.
They included about 4,000 fighters who would form the core of Sinai Province, which was called Ansar Beyt al-Maqdis before declaring its support for Islamic State last year, said the officials.
The crackdown on Islamists by Sisi - now president - led to many militants being killed, jailed or fleeing for countries like Syria and Libya.
Sinai Province now consists of only hundreds of militants scattered into groups of 5-7 men, which have few links to reduce the chances of capture, said the officials.
"They are very secretive," one of the intelligence officials said. "Each cell doesn't know about other cells." Another said: "It's a small number of militants but it takes just one person to carry out a suicide bombing." Last year, security officials said Masri and a few other leaders had been killed.
He later appeared in a video purported to prove he is alive and reaffirmed his loyalty to Baghdadi. Masri could be seen kneeling beside weapons he said were seized from 30 Egyptian soldiers killed in an attack.
A military armoured personnel carrier burned in the background.
A tribal leader in the Sinai told Reuters he had recently noticed pro-Islamic State militants driving around in new Toyota Land Cruisers. Some had Apple computers.
"It seems they are getting more and more ambitious," he said.
