Egypt pushed back Saturday against international suspicions that a bomb downed a Russian plane in the Sinai, as investigators said the cause of the crash that killed 224 was still unknown.
Initial observations from the cockpit voice recorder on the Airbus A-321 were made public amid intensifying restrictions on air travel that threatened to cripple Egypt's vital tourism industry.
In the Red Sea resort of Sharm el-Sheikh, from where the doomed airliner took off on October 31, thousands of Russian and British tourists waited for word of when they could fly home.
In Cairo, the Egyptian head of the technical investigation committee told reporters the cause of the crash a week ago was still not known.
"Initial observations... do not allow for identifying the origin of the in-flight break-up" of the aircraft 23 minutes and 14 seconds after it departed from Sharm, Ayman el-Mokkadem said.
"A noise was heard in the last second" on the voice recorder, he told a press conference.
"A spectral analysis will be carried out by specialised labs in order to identify the nature of this sound."
On Friday, Moscow halted all Russian flights to Egypt, while London has stopped British flights to Sharm. Empty aircraft are being sent out to bring stranded holidaymakers home but the process will be slow.
Russia will send 44 planes to repatriate its nationals, the Russian Federal Air Transport Agency said.
Of 11 British aircraft on standby in Cyprus earlier Saturday, three remained and were expected to depart Sunday to pick up stranded British tourists, airport officials said.
Two aircraft left Cyprus for Sharm on Saturday afternoon but six flew back to Britain empty.
- Reliant on tourism -
Sources in France close to the investigation told AFP that black box data pointed to a bomb exploding and of a sudden, violent demise of the Airbus.
British Prime Minister David Cameron has said a bomb "had more likely than not" been the cause of the disaster.
Egyptian Foreign Minister Sameh Shoukry said earlier Saturday the inquiry had yet to establish any firm theory and that foreign intelligence that triggered the international travel restrictions had not been shared with Cairo.
Already battered by years of unrest, Egypt is heavily reliant on tourism and fears the effect on the industry if it is found that a bomb caused the crash.
Russians comprise the bulk of tourists who visit Red Sea resorts such as Sharm el-Sheikh each year, and nearly 80,000 are currently in Egypt, a Russian official told AFP.
Repatriations will be spread over the coming fortnight after President Vladimir Putin's decision to halt Russian flights to Egypt.
Signup to our newsletter and follow us on Facebook and Twitter!
"Tourists will be returning from Egypt to Russia when they planned to," said Deputy Prime Minister Arkady Dvorkovich.
Russia followed Britain in saying that holidaymakers would return home without hold luggage which will be flown separately.
That restriction has prompted Egypt to limit the number of daily repatriation flights because it says there is only so much baggage left behind its airports can accommodate.
"It's going to be a long wait," said tourist Maria Chernova.
Nine flights carrying some 1,500 people were expected back in Britain Saturday, but the British government warned that some tourists may have to stay on longer before they can be flown home.
- Samples taken -
Around 19,000 Britons are thought to be still in Sharm.
"I have to fly out today at any cost; my son is getting married tomorrow, and I am still here," said a desperate Jane Kelly.
Kremlin spokesman Dmitry Peskov told news agencies the decision to restrict flights did not mean Moscow believed that the crash -- the worst aviation disaster in Russia's history -- was due to an attack.
The head of Russia's emergencies ministry said Russian experts had taken samples from the crashed jet and were testing it for any traces of explosives.
A source in Paris close to the investigation told AFP the black box data "strongly favours" the bomb theory.
Another person close to the case said the plane suffered "a violent, sudden" end, saying: "Everything was normal during the flight, absolutely normal, and suddenly there was nothing."
The Islamic State group said it downed the plane in retaliation for Russian air strikes in Syria, but has not said how.
If it was behind the attack, it would be the first time the jihadists, who control large areas of Syria and Iraq, have hit a passenger plane.
US President Barack Obama has said Washington is "seriously" considering the possibility of a bomb on board.
Homeland Security Secretary Jeh Johnson said security screenings of US-bound flights from some Middle East airports would be stepped up as a precaution.
Meanwhile, British media reported that a Thomson Airways plane heading for Sharm came within 1,000 feet (300 metres) of a missile in August, but British authorities concluded it was not a "targeted attack" and was connected to Egyptian military exercises.
An Egyptian foreign ministry spokesman called the missile allegation "preposterous", saying on Twittter it involved only ground-to-ground fire in an exercise airlines had been told about in advance.