© Maxim Grigoryev / RIA Novosti
The British government says that it believes the Russian passenger jet that crashed over Egypt's Sinai on Saturday might have been brought down by an "explosive device."

All flights from Egypt's Sharm el-Sheikh resort to the UK have been delayed as a precautionary measure, the joint statement from the Prime Minister's Office, the Department for Transport and Foreign & Commonwealth Office said.

This will allow time for a team of UK aviation experts to assess the security situation in the resort from where the Russian-operated Airbus 321 departed Saturday.

"While the investigation is still ongoing we cannot say categorically why the Russian jet crashed. But as more information has come to light we have become concerned that the plane may well have been brought down by an explosive device," the statement read.

The security assessment is expected to be completed by Wednesday night.

Since the Airbus A321 belonging to the Russian Metrojet air carrier crashed in Egypt, British officials "have been following the investigation closely... to ensure the safety of British citizens on flights from Sharm," the joint statement said.

Earlier on Wednesday, Downing Street announced that British PM David Cameron and Egyptian President Abdel Fattah el-Sisi had discussed the Russian plane crash in Sinai in a phone conversation. The two officials "agreed it was important not to prejudge the investigation," but with the cause of the crash still uncertain, they decided "it would be prudent to ensure the tightest possible security arrangements at Sharm el-Sheikh airport."

The Egyptian leader had said earlier that speculation that Islamic State might be behind the Russian plane crash was "false propaganda" aimed at damaging Egypt's image.

Extra consular staff will be deployed to the Egyptian resort, UK officials said, adding that they will be "on hand at the airport, working with the airlines, to assist British holidaymakers there."

A source close to the Egyptian investigation decoding the black boxes said that an explosion could possibly have caused the crash, Reuters reported, adding that it was unclear whether such a blast would have been the result of a bomb or fuel explosion.

Citing sources in Egypt's investigative committee, Egypt's Al-Masry Al-Youm newspaper reported on Wednesday that the decoded black boxes showed that an engine blast had caused the plane to crash, killing all 224 people on board.

With no distress signal sent from the plane to the flight's control center, the anonymous source told the media that the explosion had been huge and could have affected all the engines at once. "The investigation did not point yet to have any links to terrorists," Al-Masry Al-Youm cited its source as saying, adding that samples from the wreckage and the bodies had been taken to determine whether any explosive materials were present on the plane, or if the blast was the result of a mechanical failure.

On Tuesday, an Egyptian doctor who examined the victims' bodies suggested that "a powerful explosion took place aboard the plane before it hit the ground." The nature of the injuries led him to make such a claim, the doctor said.

Security has been beefed up at Sharm el-Sheikh airport, the Telegraph reported, adding that policemen with bulletproof vests were checking cars entering from outside the hub on Wednesday.

On the day of the crash, the Islamic State (IS, formerly ISIS/ISIL) terrorist group claimed responsibility for bringing down the plane. Another Islamic State video released on Tuesday showed a Slavic-looking and Russian-speaking jihadist praising his "Sinai brothers" in Egypt's Sinai Peninsula for "taking down" the Russian jet and threatening more attacks in retaliation for Russia's air campaign against IS in Syria.

The terrorists' claims have been dubbed by Moscow and Cairo as "unlikely," with officials saying the terrorist group does not possess the means to shoot down a plane at the altitude at which the Airbus was flying.