99% certain that bomb downed Russian plane - U.S. officials

(CNN) The U.S. appears to be increasingly confident that a terrorist bomb brought down the Russian passenger jet that broke apart over Egypt.

The growing belief was indicated by several senior U.S. officials in the intelligence, military and national security community who spoke to CNN on Saturday.

One official said it was "99.9% certain," another said it was "likely."

The remarks are stronger than those made by President Barack Obama on Thursday when he said there was "a possibility" a bomb was on Metrojet Flight 9268, which disintegrated over the Sinai Peninsula on October 31, killing all 224 people aboard.

The view also contrasts with the cautious stance taken by Egyptian officials, who are in charge of the main investigation into the air crash and insist that no conclusion has been reached yet.

"All the scenarios are out on the table," Ayman al-Muqaddam, the head of the investigation, told reporters Saturday. "We don't know what happened exactly."

ISIS chatter analyzed

The belief that a bomb was most likely to blame centers to a large extent on British and U.S. intercepts of communications after the crash from the Islamic militant group ISIS' affiliate in Sinai to ISIS operatives in Syria, according to officials.

The Sinai affiliate has publicly claimed responsibility for downing the Russian jet, which was flying from the Red Sea resort of Sharm el-Sheikh to St. Petersburg, but so far hasn't explained how it was done. That's prompted questions about the claim among some observers, considering ISIS' tendency to often publicize its acts for propaganda value.

The ISIS messages monitored by British and American intelligence agencies are separate from the group's public claims, a U.S. official has said.

The two Western countries have been analyzing the specific language in the chatter to determine to what extent the operatives were talking about the type of bomb and detonator used, and whether that language was a true representation of what happened, one official told CNN.

Several officials said it's the specificity of the chatter that has directly contributed to the U.S. and British view that a bomb was most likely used.