The cause of the destruction of a Russian commercial airliner Saturday over Egypt remains unclear. The plane fell in pieces in the war-torn region of Hasana in northern Sinai, killing all 224 people on board.

The jetliner crashed to earth in a state of disintegration, having largely broken up in midair, and scattering debris over a wide area.

The Islamic State (IS) affiliate in the Sinai Peninsula claimed responsibility for the attack on Saturday. These claims prompted immediate expressions of skepticism from Egyptian and Russian officials. ISIS is not known to possess anti-aircraft weapons with sufficient range to carry out an attack against a jet flying at cruising altitude, according to officials and experts cited in Western media.

Some military analysts have suggested that the available evidence points to a bomb planted inside the plane’s hold, saying that an attack could have been similar to that which destroyed Pan Am 747 over Lockerbie, Scotland in 1988.

Some reports in the Russian media have suggested that the plane may have been destroyed by a mechanical failure resulting from poor maintenance, with reports circulating of a pre-flight phone call in which the pilot worried to his wife about the condition of the aircraft.

Metrojet, the company servicing the flight, has maintained that the plane was destroyed by some “external” cause, saying that its own investigation has ruled out a mechanical failure as the reason.

“We rule out technical fault of the plane or the pilot’s error, the only explainable cause is physical impact on the aircraft,” Metrojet executive Alexander Smirnov said.

The company’s claims are predictable, given the immense financial interests at stake. Aviation experts have already criticized Metrojet, however, saying that the company’s claims were advanced far too quickly and without any basis in evidence.

“That statement is premature and is based on no real facts,” Alexander Neradko of Russia’s Air Transport Agency told Egyptian media on Monday.

“We know that components of the plane have been thrown over a wide area. That says the breakup took place in the air, at a high altitude. But it is very premature to talk about the reasons,” Neradko said.

“I am surprised that an airline manager, at the point that we are at in this investigation, would make a statement like that,” said Robert Francis, a former official with the National Transportation Safety Board in the United States.

“Without the flight recorders having been read, and without more investigation of the fuselage, which is spread all over the place, I don’t think you can rule out anything,” Francis said.

While a number of international carriers have suspended flights over the area, others have not. US-based carrier United Airlines has continued routing flights over the Sinai, saying that the company “sees no need” to stop the flights.

Given the timing and the nationality of the jet, coming amidst a major escalation of Russia’s military presence in Syria, an attack on the plane is a definite possibility.

Russian actions in Syria have been directed at a number of US-backed terrorist groups, variously affiliated with factions of al Qaeda, that have been built up by Washington as part of efforts to overthrow the government of Bashar al-Assad. These groups have been armed to the teeth by the US and its allies, and have received more advanced weaponry since the onset of Russia’s military campaign in Syria. ISIS is itself an offshoot of the US-backed civil war in Syria.

Russian leaders have clearly been concerned to muffle speculation along these lines. Russian President Vladimir Putin called the incident a “great tragedy,” and called for investigators to outline an “objective picture” of the crash.

The US government, usually the first to play the terrorist card under these circumstances, has sounded a noticeably more muted tone. On Monday, US Director of National Intelligence James Clapper made remarks downplaying claims that IS militants were behind the incident.

“It’s unlikely, but I wouldn’t rule it out. We don’t have any direct evidence of any terrorist involvement, yet,” Clapper said.

Whatever its origins, the incident will likely become a further blow against Egypt's tourism sector, which has already contracted by some 20 percent this year. The industry was already reeling from an incident earlier this year, when Mexican tourists who were traveling in a caravan in Egypt’s Western Desert were killed by an Egyptian military helicopter.