A US official said on Wednesday that the latest US intelligence suggests that the crash of Metrojet Flight 9268 was most likely caused by a bomb on the plane planted by ISIS or an ISIS affiliate, according to a CNN report. The Russian commercial airline crashed in Egypt's Sinai on Saturday, killing all 224 passengers on board."There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane," the official told CNN. The source emphasized that there has not been a formal conclusion reached by the US intelligence community but the assessment that ISIS was involved was reached by "looking back at intelligence reports that had been gathered before Saturday's plane crash and intelligence gathered since then," the American news outlet reported. The official said that the US did not have credible or verified intelligence of a specific threat prior to the crash, but that, "prior to the incident, "there had been additional activity in Sinai that had caught our attention."CNN quoted another US official who said the intelligence regarding ISIS is in part based on monitoring of internal messages of the terrorist group, separate from public ISIS claims of responsibility following the incident. Britain said earlier on Wednesday that the Russian plane that crashed after taking off from the resort town 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," it added.As a precautionary measure, the government has decided that flights due to leave Sharm for Britain on Wednesday evening will be delayed to allow time for a team of UK aviation experts, currently traveling to Sharm, to make an assessment of the security arrangements in place at the airport.