The cause of a Russian plane crash in Egypt on Saturday is looking more like an explosion, an Egyptian source close to the investigation of the black boxes said yesterday.

“It is believed to be an explosion but what kind is not clear. There is an examination of the sand at the crash site to try and determine if it was a bomb,” the source said.

“There are forensic investigations underway at the crash site. That will help determine the cause, to see if traces of explosives are found.”

Egypt has dismissed claims by Islamic State that it brought down the aircraft with 224 passengers and crew aboard.

The country’s aviation ministry said earlier the cockpit voice recorder from the plane was partially damaged but that black box data had been extracted and validated and was being analysed.

Meanwhile Britain also said yesterday that the Russian plane that crashed in Egypt after taking off from Red Sea resort of Sharm al-Sheikh might have been brought down by an explosive device.

“While the investigation is still ongoing we cannot say categorically why the Russian jet crashed,” Prime Minister David Cameron’s office said in a statement.

“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.”

As a precautionary measure, it said, the government had decided that flights due to leave the resort for Britain yesterday evening would be delayed to allow time for a team of UK aviation experts to make an assessment of the security arrangements in place at the airport.

The Russian-operated Airbus A321M crashed shortly after taking off from the resort on its way to St Petersburg, killing all 224 people on board.

In another development yesterday Islamic State’s Egyptian affiliate dismissed in an audio message doubts that it had downed a Russian passenger plane over Egypt’s Sinai Peninsula, killing all aboard, and said it would tell the world how it did so in its own time.

We, with God’s grace, are the ones who brought it down

Sinai Province, an Egyptian group loyal to Islamic State, said in a statement the same day that it had brought down the airliner “in response to Russian air strikes that killed hundreds of Muslims on Syrian land”.

The claim has been dismissed by Russian and Egyptian officials. Security experts and investigators have said the plane is unlikely to have been struck from the outside and Sinai-based militants are not believed to possess the technology to shoot down a jet from a cruising altitude above 30,000 feet. In an audio message posted on a Twitter account used by the group, Islamic State’s Egyptian affiliate insisted it was behind the crash.

“We say to the deniers and the doubters: Die from your frustration. We, with God’s grace, are the ones who brought it down, and we are not obliged to disclose the mechanism of its demise,” the speaker said.

“So go to the wreckage, search, bring your black boxes and analyse, give us the summary of your research and the product of your expertise and prove that we did not bring it down or how it came down,” he said.

“We will disclose the mechanism of its demise at the time that we want and in the way that we want.”

Russia, an ally of Syrian President Bashar al-Assad, launched air raids against opposition groups in Syria including Islamic State on Sept. 30. The hardline group has called for war against both Russia and the US in response to their air strikes in Syria.

Islamic State backers in Iraq issued a video on Tuesday congratulating their Egyptian colleagues and warning Russian President Vladimir Putin that more was to come. They handed out sweets to celebrate the crash.

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