Russian plane black boxes point to 'attack', Putin halts flights

Meanwhile, British airlines were scrambling to evacuate passengers in Sharm el-Sheikh after cancelling flights to the Red Sea resort from which the doomed Airbus took off.

The flight data and voice recorders showed "everything was normal" until both failed at 24 minutes after takeoff from the Sharm el-Sheikh resort Saturday, pointing to "a very sudden explosive decompression," one source said.

The Islamic State group claimed it down the plane, providing no details, saying it was retaliation for Russian air strikes in Syria.

The data "strongly favours" the theory a bomb on board brought down the plane, the source added.

Another source said the plane had gone down suddenly and violently.

One of the black boxes showed that the plane suffered "a violent, sudden" end, a source close to the case in Paris told AFP.

The flight data recorder showed that "everything was normal during the flight, absolutely normal, and suddenly there was nothing".

President Vladimir Putin ordered flights halted , although Moscow had previously downplayed reports that a bomb caused the crash.

Kremlin spokesman Dmitry Peskov told news agencies the measure did not mean Russia believed it was an attack as the investigation continued.

Meanwhile, 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.

Russia's Interfax news agency quoted a representative of the national Aeroflot carrier as saying a plane would be sent Friday to pick up stranded Russians.

With international concerns mounting, European airlines prepared to bring home thousands of tourists from the Red Sea resort, which has been a jewel in Egypt's tourism crown.

A first flight landed at London's Gatwick airport Friday afternoon, after a lengthy delay to its departure. Another plane was also headed for Britain.

There were angry scenes in Sharm el-Sheikh, as thousands of anxious Britons, who had also hoped to fly home, were sent back to their hotels after Egypt blocked several other repatriation flights.

British Ambassador John Casson was heckled as he announced the news.

Egyptian Aviation Minister Hossam Kamal said only eight of 29 flights would take off because the airport could not cope with all the luggage left behind.

He and the head of the Egyptian-led probe into the incident are to hold a press conference on Saturday at 1500 GMT, the government's press office said, before warning that it may be "postponed."

In a sign of mounting fears about the security of baggage handling in Egypt, Dutch carrier KLM announced that it had banned check-in luggage on an early flight from Cairo, mirroring moves taken by several European airlines.

And American Homeland Security chief Jeh Johnson said the United States would step up security screenings of US-bound flights from some Middle Eastern airports.

Cairo has sought to downplay any suggestion of an attack.

But US President Barack Obama said: "I think there is a possibility that there was a bomb on board and we are taking that very seriously," while emphasising it was too early to say for sure.

In London, Prime Minister David Cameron told reporters it was "more likely than not that... a terrorist bomb" caused the crash.

And The Times newspaper reported that electronic communications intercepted by British and US intelligence suggested a bomb may have been carried onto the plane.

Satellites uncovered chatter between militants in Egypt's Sinai Peninsula and Syria, it said.

"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.

Egypt has beefed up security at airports to "give confidence to the British government, but that does not mean we concur with any scenario," foreign ministry spokesman Ahmed Abu Zeid said.

There is no global or European blanket ban and some flights have continued from the airport.

France and Belgium have warned citizens against travelling to Sharm el-Sheikh. and Britain has advised against all but essential travel by air to or from the resort.

The British government authorised flights to resume from the resort on Friday to bring home an estimated 20,000 British tourists.

But thousands were turned away after Egypt blocked British tour operators from flying in empty aircraft to make up the backlog.

Those passengers who did fly out were allowed to carry hand luggage only, with their check-in bags to follow separately.

Joining a string of airlines in avoiding Sharm el-Sheikh, Lufthansa said its Eurowings subsidiary would halt flights between Germany and the Red Sea resort, while Turkish Airlines also cancelled two flights.

If it was behind the attack, it would be the first time IS, which controls large areas of Syria and Iraq, has hit a passenger plane.