Islamic State (IS) leaders celebrated the downing of the Russian airliner that crashed in Egypt, according to communications intercepted by US intelligence, NBC has reported.

Communications between IS leaders in Raqqa, Syria and persons in the Sinai Peninsula included boasts about the Airbus A321M, operated by Metrojet, which crashed on Saturday en route to St Petersburg from the Red Sea resort of Sharm al-Sheikh, killing all 224 people on board.

"They were clearly celebrating," NBC Nightly News quoted a US official as saying.

Key points: Officials say intercepted 'chatter' suggests a bomb brought down Russian plane in Egypt

Officials say intercepted 'chatter' suggests a bomb brought down Russian plane in Egypt Assessment involved communications intercepted from militants and one or more governments

Assessment involved communications intercepted from militants and one or more governments Russia suspends all flights to Egypt

Russia suspends all flights to Egypt Flights to evacuate Britons from Sharm al-Sheikh resume

The "chatter" included a boast of taking down the plane on Saturday and how it was done.

The US intelligence community intercepted a message from a Sinai group affiliated with IS that warned of "something big in the area" before the jet crash.

Earlier, British and US spies said they had intercepted "chatter" suggesting that a bomb, possibly hidden in luggage in the hold, downed the plane.

Western intelligence sources said some of the assessment about the bomb came from intercepted communications both from suspected militants and from one or more governments involved in the investigation.

The intelligence sources, who spoke on condition of anonymity due to the sensitivity of the situation, said the evidence was not categorical and that there is still no hard forensic or scientific evidence to support the bomb theory.

"We still cannot be categorical but there is a distinct and credible possibility that there was a bomb," one source said.

Two sources with knowledge of the matter said the bomb may have been hidden in luggage in the hold of the Russian plane. They refused to give any further information.

A US official said the "chatter" intercepted about the bomb includes conflicting details about whether the bomb was placed on the plane.

The Times newspaper said the information came to light after a joint US-British intelligence operation "used satellites to uncover electronic communications" between Islamic State group militants in Syria and Egypt, without giving a source for the information.

Loading...

"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 said.

Meanwhile, a source close to the investigation said an analysis of black boxes from the plane "strongly favoured" the theory a bomb exploded onboard the aircraft.

The flight data and voice recorders showed "everything was normal" until both failed at 24 minutes after takeoff, pointing to "a very sudden explosive decompression", the source said.

Russia suspended all flights to Egypt as a result of the reports leaving more than 45,000 Russians stranded.

Tourism officials have predicted it could take up to a month to bring everyone home.

After British prime minister David Cameron was shown intelligence indicating it was likely the plane was brought down by a bomb he halted flights to and from Sharm al-Sheikh but reinstated some flights on Friday.

Britain said there was a "credible threat" but refused to comment further on the intelligence involved, citing long-standing rules about disclosing operational details about live investigations.

Russia was initially critical of Britain's assessment to suspend all flights however president Vladimir Putin ordered the halt to flights after Alexander Bortnikov, the head of Russia's FSB security service, recommended Russia suspend all passenger flights to Egypt until it knew exactly what caused the crash.

He also ordered officials to draft a mechanism for evacuating Russian citizens from the country.

An image released by Russia's emergency ministry shows the wreckage of a A321 Russian airliner in Egypt. ( AFP: Russia's Emergency Ministry/Maxim Grigoryev )

Evacuation flights finally leave but situation 'difficult'

Britain said it was working with Egyptian authorities to bring tourists in Sharm al-Sheikh back to the UK safely, but said the situation was "difficult and fluid".

An estimated 20,000 British nationals are on holiday in the region.

Some evacuation flights resumed on Friday, with airlines laying on extra planes to get stranded travellers home, but passengers would only be allowed to fly with hand luggage due to a British government request.

Earlier, budget airliner easyJet said Egyptian authorities had suspended British airlines from flying into the resort, a claim denied by Egypt's civil aviation ministry.

"The British airline wants to schedule 18 flights at the same time and wants to transport British passengers from Sharm al-Sheikh without their luggage, which we would have to transport later," civil aviation minister Hossam Kamal said.

"This constitutes a huge burden on the airport because its capacity does not allow for that. We have asked them to organise eight flights only and one plane will transport luggage."

British ambassador to Egypt John Casson echoed Mr Kamal's comments about the scale of the operation and said progress was being made in transporting tourists back.

"Flights are coming in which will allow us to take more people home today," Mr Casson said.

As he spoke, he said the first two flights to Britain had already boarded and were due to take 180 passengers each.

"There are just some challenging logistical issues involved in making sure that flights can leave and arrive in a busy airport in line with international regulation in a way that is safe," he said.

"We are working through these issues."

US steps up airport security after Egypt crash

The United States has made moves to step up security screenings of US-bound flights from some Middle East airports as a precaution.

Homeland Security Secretary Jeh Johnson said the US would review its assessments of certain foreign airports and offer them help with security.

The US will also take other measures "both seen and unseen".

Mr Johnson said the facts and circumstances surrounding the crash were still under investigation, although US president Barack Obama has acknowledged the "possibility there was a bomb on board."

The US security measures have been described as "interim, precautionary enhancements to aviation security".

Mr Johnson said expanded screenings would be applied to items on aircraft, airport assessments would be enhanced in conjunction with US international partners, and offers of help would be made to beef up aviation and airport security.

"At this time these security enhancements are intended only for certain foreign airports in the region," he said in a statement.

A map of the Sinai Peninsula in Egypt shows the flight path of the Airbus A321. ( RNGS Reuters )

ABC/AFP/Reuters