Last Updated Nov 5, 2015 7:09 AM EST
CAIRO -- The Egyptian minister for civil aviation insisted Thursday that its airport security is up to international standards, and said there was no evidence yet to support the theory that a bomb was planted on the Metrojet plane that came apart over Egypt's Sinai Peninsula.
"The investigation team does not have yet any evidence or data confirming this hypothesis," Hossam Kamal said.
His remarks came a day after a startling admission in London -- which tied in with claims of responsibility from a Sinai-based ISIS affiliate -- at the end of a special meeting of the British cabinet's crisis committee.
Foreign Secretary Philip Hammond didn't mince words: "We've looked at the broad picture of information available to us, including intelligence, and we have concluded from that that there is a significant possibility that the Russian aircraft was brought down by an explosive device on board."
CBS News correspondent Allen Pizzey says new video, reportedly taken shortly after the crash, shows smoke rising from the wreckage as Egyptian ambulance workers move around the scene.
Officially, U.S. intelligence agencies have declined to speculate on the cause in order not to prejudice the ongoing investigation.
Off the record, however, intel sources have told CBS News they're leaning toward the bomb theory, based at least in part on "chatter" between ISIS suspects on social media.
Speaking the day after Hammond, British Prime Minister David Cameron didn't appear too eager Thursday to back down from the assessment of the previous day, referring to "the intelligence and information that we have that gave us the concern that it was more likely than not a terrorist bomb."
Cameron stressed that British agencies "don't know for certain that it was a terrorist bomb. There is an investigation taking place in Egypt. We need to see the results of that investigation."
Thursday morning, CBS News security contributor and former deputy CIA chief Mike Morell said he believed the remarks coming out of London were "overestating the possibility of a bomb at this point."
"I would not say there is a strong possibility of bomb," Morell said on "CBS This Morning," noting that placing a bomb on a commercial aircraft is a "pretty sophisticated operation," and that if ISIS' affiliate in Sinai managed to do it, it would be the largest bombing of an aircraft in 25 years.
A flight tracking website shows the Russian plane plunging to the ground at 300 miles an hour.
Aviation consultant Denny Kelly says, if there was a bomb on the Airbus A321, the wreckage and bodies will provide the evidence.
"There are going to be certain types of markings on the body, and there's going to be certain types of things, certain markings inside the airplane," he said, adding that such evidence "can readily be discovered at the scene if the people know what they're doing."
The tail section of the plane was found nearly three miles from the main fuselage, reinforcing the theory that it could have broken off in flight due to damage caused 14 years ago when the plane suffered what is known as a "tail strike," the tail of the plane hitting the ground before the wheels on landing.
A bomb could have the same effect, but with little firm evidence thus far of an explosion, other than two flashes picked up by a U.S. infrared satellite, Russian officials have warned all week against speculation.
Meanwhile, a jetliner from the same airline, Metrojet, which used to be known as Kolgalymavia before a rebranding, was crippled Thursday as it taxiied at an airport in St. Petersburg, Russia, from which it was attempting to depart for Egypt.
Metrojet issued a statement saying the plane's nose landing gear was damaged while the jet was attached to a tractor to move it around near the terminal.
The airline said it was the fault of ground crew member driving the tractor, but Pulkovo airport released a statement saying the pilot of the plane caused the damage by applying the breaks when he shouldn't have. The flight was delayed for several hours.
Russian investigators said Thursday they were wrapping up the search of the Metrojet crash area in Sinai.
Teams analyzing the flight data and cockpit voice recorders -- the latter of which reportedly sustained damage -- could have as much as a month of work left, however.
They're urging patience and saying nothing about bombs, or anything else.