Alexander Smirnov, the deputy general director of Kogalymavia, which operates flights under the name Metrojet, said on Monday that the disaster was most likely caused by an external "impact". "The only plausible reason can be a mechanical impact on the plane," Smirnov told a press conference. "There is no combination of system failures that could cause the plane to be destroyed in the air," he was quoted as saying by the Interfax news agency.

...[he] told journalists that the company has “completely excluded technical error and an error on the part of the pilot” as possible causes for the crash.

(Yes, Kogalymavia, Metrojet, Russia and Egypt all have dogs in this fight and are apt to spin things -- and Russian and Egyptian officials are taking different positions, but experts from multiple countries are working with them.)

Some media remain fixated on Wilayat Sinai's access to weapons and not having one that should shoot down a plane flying at such a high altitude. But the statement never said how it caused the plane to come down.

The Independent last night:

The group’s Egyptian affiliate, Wilayat Sinai, said it downed the plane in revenge for Russian air strikes in Syria but experts pointed out missile systems controlled by the militants only have a range of 15,000ft – half the plane's altitude.

There are other possibilities to focus on, rather than rehashing the capability of manpads. There must be a number of ground crew who had access to the plane before it took off. One could have planted the bomb.

Yves Trotignon, a former French intelligence agent, noted that ISIS's claim of responsibility was vague in detail. "The statement does not say they shot it down, but that they destroyed it," he told Le Parisien. "You could imagine explosives on board, or sabotage."

Terrorism experts said Isil had never claimed an attack it did not carry out. Mathieu Guidere, professor of Islamic studies at the University of Toulouse, said ISISl "is very well established in the Sinai, has infiltrated almost all organisations and infrastructure, so it is quite possible that a fighter sabotaged the plane at the airport before it took off or placed a device on board".

If so, I think in a few days we'll see a "mea culpa" video by the perpetrator, coupled with a pledge to ISIS, just as happened with past terror incidents abroad.

Another possibility: The bomb was placed on board and the flight tracked by ISIS online, which then activated the bomb by mobile phone when it was over Sinai. A few weeks ago, Russia busted an ISIS cell in Moscow planning a bomb attack on public transport. One of those arrested said the plan was to activate the bomb by mobile phone.

In March, an ISIS training manual surfaced on the internet, How To Survive In The West: A Mujahid ("jihadi fighter") Guide. "Instructions are also given for how to make nail bombs, cell-phone detonators, and "primitive car bombs," as well as how to transport them to targets."

On a related note, U.S. personnel have also been the target of ISIS attacks in Sinai. in September, 4 U.S. troops in Sinai were injured by an IED.

For months, the nearly 700 American soldiers deployed on the ground in Egypt's Sinai Peninsula have weathered a crisis all but indistinguishable from their fellow troops in Iraq.

Living amid blast walls topped with razor wire, riding only in up-armored vehicles, the troops face a constant threat of attacks from extremist groups loyal to the so-called Islamic State.

After the IED hit the troops, the U.S. response was:

"The U.S. is concerned over deteriorating security conditions in an area of Northeastern Sinai where Egyptian security forces as well as civilian and military elements of the MFO, including the U.S. military forces stationed at the MFO North Camp, are exposed to potential risk," said Army Maj. Roger Cabiness, a Pentagon spokesman.

"The U.S. has been working closely with the government of Egypt and with the MFO to help address those risks," Cabiness said.

It wasn't ISIS' first attack on the compound:

On June 9, the North Camp was hit by rockets and mortars. The ISIS-linked group claimed it targeted the MFO base in part because its airport is used by "Crusader forces to maintain the security of Jews," according to a report from the Institute for the Study of War in Washington, D.C.

That attack on an "international target" was a "major shift" for the ISIS branch in the Sinai, which had previously limited its attacks to the Egyptian military. That may "signal the approach of a broader strategy by Wilayat Sinai to deter U.S.-led coalition involvement in Iraq and Syria, or to divert international attention away from a main offensive in Iraq or Syria,” according to the ISW report.

More on that here.

Back to Wilayat Sinai and its weapons: Sinai-based ISIS militants have been using advanced weaponry, including Russian Kornet anti-tank missiles and SA-18 anti-aircraft weapons. Here are some shots of it taking Russian Kornets from Baji Air Base after a raid, and some photos showing members of Wilayat Sinai ISIS using them.