In an interview with Sky News, British Prime Minister David Cameron said a Russian airliner was "more likely than not" downed by a bomb.
Cameron also told the network that there was a "significant possibility" that the Islamic State was responsible.
On the BBC, Cameron said: "We cannot be certain that the Russian airliner was brought down by a terrorist bomb, but it looks increasingly likely that that was case."
Of course, this comes just after British authorities suspended flights to and from Sharm el-Sheikh in Egypt, citing security concerns.
As we've reported, Metrojet Flight 9268 broke up midair over the Sinai Peninsula, killing all 224 people aboard.
The Washington Post reports that Egypt and Russia called the British suggestion mere "speculation." The Post adds:
"Egypt's civil aviation ministry said in a statement Thursday that the British theory of a bomb having been smuggled aboard the plane 'is not based on facts,' and that all of the country's airports apply international security standards.
"'The investigation team does not have any evidence or data confirming this hypothesis,' Civil Aviation Minister Hossam Kamal said, according to the statement."
On the record, the Director of National Intelligence James Clapper said the U.S. can't rule out the possibility that the crash was brought down by terrorists.
CNN spoke to several unnamed U.S. officials who said they believe the plane was likely downed by a bomb planted by the Islamic State or associates. The network reports:
"The signs pointing to ISIS [or the Islamic State], another U.S. official said, are partially based on monitoring of internal messages of the terrorist group. Those messages are separate from public ISIS claims of responsibility, that official said.
"In an audio message from ISIS' Sinai branch that was posted on terror-related social media accounts Wednesday, the organization adamantly insisted that it brought down the flight.
"'Find your black boxes and analyze them, give us the results of your investigation and the depth of your expertise and prove we didn't do it or how it was downed,' the message said. 'Die with your rage. We are the ones with God's blessing who brought it down. And God willing, one day we will reveal how, at the time we desire.'"