ST. PETERSBURG, Russia — Only an external impact could have caused a Russian plane to dive into the Egyptian desert, killing all 224 people on board, the airline said Monday, adding to a series of incomplete and confusing statements from investigators that left unclear why the plane broke up in mid-flight.

“We rule out a technical fault of the plane or a pilot error,” said Alexander Smirnov, deputy general director of Metrojet. “The only possible explanation could be an external impact on the airplane.”

But when pressed for more details about the type of impact and what could have caused it, Smirnov insisted that he was not at liberty to discuss details because the investigation was ongoing. He also did not explain whether he meant something had hit the plane or that some external factor caused the crash.

Viktor Yung, another deputy director general of Metrojet, said the crew did not send a distress call and they did not contact traffic controllers before the crash.

An Egyptian official had previously said the pilot radioed that the plane was experiencing technical problems and he intended to try to land at the nearest airport.

The Airbus A321-200 crashed from 31,000 feet in the Sinai Peninsula just 23 minutes after taking off from the Egyptian Red Sea resort of Sharm el-Sheikh en route to St. Petersburg.

Smirnov said the plane dropped 300 kph (186 mph) in speed and 1.5 kilometers (about 5,000 feet) in altitude one minute before it crashed.

Alexander Neradko, head of Russia’s federal aviation agency, told reporters on Sunday that the large area over which plane debris fragments were found indicates the jet disintegrated while flying at high altitude. He would not comment on any possible reason for the crash, citing the ongoing investigation.

When planes do break up in midair, experts say it’s usually because of one of three factors: a catastrophic weather event, a midair collision or an external threat, such as a bomb or a missile.

With no indication that those events played a role in the crash, Todd Curtis, a former safety engineer with Boeing, said investigators will be looking at more unusual events, such as an on-board fire or corrosion that caused a structural failure.

A local affiliate of the extremist Islamic State group has claimed it brought down the aircraft, which crashed in the northern Sinai, where the Egyptian military and security forces have battled militants for years. Russian officials have dismissed that claim as not credible.

British military analyst Paul Beaver said he thought the crash was most likely caused by a bomb on board, saying he was certain IS does not possess a missile system — such as the Russian BUK — capable of hitting the plane.

“I’m pretty convinced that ISIS doesn’t have a ‘double-digit’ SAM (surface-to-air missile) that is necessary to go up as far as 31,000 feet,” he said, using an alternative acronym for the terror group. “That’s a very serious piece of equipment, and I don’t think they have that sophistication.”

He also said the Sinai desert is well-scrutinized by intelligence agencies, so a missile would have been seen.

The flight recorders will provide key information, including the plane’s airspeed and whether it was on autopilot. Russian officials were shown the black boxes found at the site of the crash in the Sinai Peninsula and emergency situations minister Vladimir Puchkov says they are in a good condition, Russian news agencies reported on Monday.

At the crash site, emergency workers and aviation experts from Russia and Egypt swept across the barren terrain Monday, searching for more victims and examining the debris for more clues as to the cause of the crash.