ST. PETERSBURG, Russia (AP) -- Only an external impact could have caused the crash of a Russian plane in Egypt that killed all 224 people on board, a top airline official said Monday, raising more questions about what exactly happened.
"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 what 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.
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.
Smirnov also 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 into Egypt's Sinai Peninsula.
The Airbus A321-200 crashed in the Sinai 23 minutes after taking off from the Egyptian Red Sea resort of Sharm el-Sheikh en route to St. Petersburg.
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.
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.
A Russian cargo plane brought the first bodies of Russian victims killed in the crash to St. Petersburg, where many of them are from. The city, awash in grief for its missing residents, is holding three days of mourning through Tuesday.
The government plane brought 140 bodies to St. Petersburg's Pulkovo airport, touching down in the dark. The bodies were then taken to a city morgue and a crematorium, where Russian forensic experts immediately began working to identify the victims, said Yulia Shoigu, a Russian Emergency Situations official.
The search for bodies at the Sinai crash site should wrap up late Monday night and another plane with more crash victims' bodies will then travel from Cairo to St. Petersburg, Emergency Situations Minister Vladimir Puchkov told a televised news conference.
President Vladimir Putin declared Sunday a nationwide day of mourning and flags flew at half-staff across the country.
Mourners have been coming to St. Petersburg's airport since Saturday with flowers, pictures of the victims, stuffed animals and paper planes. Others went to churches and lit candles in memory of the dead.
In the Sinai, aviation experts and search teams have been combing a 16 square kilometer area (more than 6 square miles) to find bodies and pieces of the jet. The Egyptian government said Sunday that 163 bodies had been recovered.
Russia has sent over 100 emergency workers to Egypt to help with the investigation into the crash, and aviation teams from France, Germany and Airbus are also working in Egypt.
Smirnov, Metrojet's deputy director, described the A321 as a reliable aircraft that would not fall into a spin even if the pilots made a grave error because its automatic systems would correct crew mistakes.
Egyptian President Abdel-Fattah el-Sissi cautioned that the cause of the crash may not be known for months.
"It's very important that this issue is left alone and its causes are not speculated on," he told a meeting of top government officials. The investigation "will take a long time" and "needs very advanced technologies."