Evidence has firmed that a Russian plane that crashed in the Egyptian desert was brought down by a bomb onboard.

The Airbus A321, headed for St Petersburg, crashed less than 25 minutes after taking off from the Sharm al-Sheikh tourist resort, killing all 224 passengers and crew.

Investigations uncovered blackbox recordings that featured “uncharacteristic” sounds immediately before the plane lost communications.

Those sounds were likely caused by a bomb, an unnamed member of the Egyptian investigation team said.

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“The indications and analysis so far of the sound on the black box indicate it was a bomb,” they said.

“We are 90 per cent sure it was a bomb.”

Islamic State militants fighting Egyptian security forces in Sinai claimed responsibility for the crash soon after the plane came down on October 31.

But Egyptian President Abdel Fattah al-Sisi dismissed the claim, and said “speculation” should be left “to specialists”.

Confirmation that militants brought down the airliner could have a devastating impact on Egypt’s lucrative tourist industry, which has suffered from years of political turmoil.

On Saturday, lead investigator Ayman al-Muqaddam said there could be other reasons for the crash, including a fuel explosion, metal fatigue in the plane or lithium batteries overheating.

British Foreign Secretary Philip Hammond said the incident could lead to changes in flight security.

“If this turns out to be a device planted by an ISIL operative or by somebody inspired by ISIL, then clearly we will have to look again at the level of security we expect to see in airports in areas where ISIL is active,” Mr Hammond told the BBC.

Russian president Vladmir Putin suspended all flights from the country to Egypt until the cause of the crash was determined.

Turkey and several European countries – including the United Kingdom – also stopped flights to the resort area and other Egyptian destinations.

About 11,000 Russian tourists returned home on Sunday, just one eighth of the 80,000 left stranded after flights were halted.

-with AAP