The latest U.S. 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 U.S. official familiar with the matter.
The official stressed that there has not been a formal conclusion reached by the U.S. intelligence community.
"There is a definite feeling it was an explosive device planted in luggage or somewhere on the plane," the official told CNN's Barbara Starr.
The assessment was reached, the official said, by looking back at intelligence reports that had been gathered before Saturday's plane crash and intelligence gathered since then.
The United States did not have credible or verified intelligence of a specific threat prior to the crash, however, the official said, prior to the incident, "there had been additional activity in Sinai that had caught our attention."
Another U.S. official said the intelligence regarding ISIS is in part based on monitoring of internal messages of the terrorist group.
Those messages are separate from public ISIS claims of responsibility, that official said.