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St. Petersburg, Russia • U.S. satellite imagery detected heat around a Russian jetliner just before it went down in Egypt's Sinai Peninsula, two U.S. officials said Tuesday. But the discovery doesn't resolve the mystery of why the plane crashed, killing all 224 aboard.

A missile striking the Metrojet Airbus A321-200 was ruled out because neither a launch nor an engine burn had been detected, one of the officials said.

The infrared activity that was detected could mean many things, including a bomb blast or that an engine on the plane exploded due to a malfunction.

Aviation analyst Paul Beaver said the heat picked up by the satellite "indicates that there was a catastrophic explosion or disintegration of the airplane," but doesn't reveal the cause.

"It doesn't tell us if it was a bomb ... there is a whole raft of things that could happen in this regard," he said.

It also could indicate a fuel tank or engine exploding, although "engines are designed so that if something malfunctions or breaks off, it is contained within the engine," Beaver added.

Both U.S. officials spoke on condition of anonymity.

Some aviation experts had suggested a bomb was the most likely cause of Saturday's crash, while some others pointed at a 2001 incident in which the jetliner damaged its tail during landing.

The Metrojet was flying from Egypt's Red Sea resort of Sharm el-Sheikh to St. Petersburg when it crashed in the Sinai Peninsula after breaking up at high altitude, Russian aviation officials said.

Islamic State militants said they had "brought down" the plane because of Moscow's recent military intervention in Syria against the extremist group. But the group did not provide any evidence to support its claim, and militants in northern Sinai have not shot down any commercial airliners or fighter jets.

Egyptian President Abdel-Fattah el-Sissi called that claim "propaganda" aimed at damaging the country's image, and he insisted the security situation in the Sinai Peninsula is under "full control."

President Vladimir Putin said Russia will keep fighting terrorism in Syria and elsewhere, adding that no one will succeed in scaring it.

His spokesman, Dmitry Peskov, rejected any connection between the crash and the Russian military action in Syria, saying there is no reason to link them.

An international team of experts prepared to analyze the plane's flight data and cockpit-voice recorders, the so-called "black boxes."

The joint investigation committee, which includes Egyptian, Russian, French and German experts as well as representatives from Ireland, where the plane was registered, was wrapping up its last field inspection at the crash site. It will start working on the recorders, said Egyptian Civil Aviation Minister Hossam Kamal.

As the investigation moved forward, more of the dead were brought to St. Petersburg. Alexei Smirnov of the Russian Emergency Situations Ministry said government planes have brought 140 bodies and other human remains so far; families have identified 19 victims.

Alexander Agafonov, head of the Russian rescue mission in Egypt, said at a televised conference that searchers found no more bodies Tuesday after combing an area of 10.8 square miles.