The cause of the Russian airliner crash in Egypt "could only have been an external impact on the plane" mid-air, a top official at the airline has said.

Alexander Smirnov, the deputy general director of Metrojet, said a technical fault or pilot error could not have caused the crash, which killed all 224 people on board.

Two days ago, Islamic State claimed responsibility for the crash.

When pressed for an explanation about what could have caused the impact, Mr Smirnov insisted that he was not at liberty to discuss details because the investigation was ongoing.

Mr Smirnov also said the crew did not send a distress call and they did not contact traffic controllers before the crash.

The Metrojet 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.

Russian officials say it broke up at high altitude, scattering fragments of wreckage and bodies over a wide area.

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

A Russian cargo plane brought the first bodies of Russian victims killed in the crash to St Petersburg, a city awash in grief for its missing residents.

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.

Russia's emergency situations minister has examined the black boxes from the crash and said they are in a good condition.

Vladimir Puchkov was quoted as saying that Russian officials were shown the black boxes found at the crash site.