Russian media reports say unusual sounds have been heard from cockpit recordings at the moment a Russian passenger plane crashed in Egypt's Sinai Peninsula at the weekend.

The news came after revelations by US broadcasters that satellite images had detected a heat flash at the time of the crash that killed all 224 people on board the Airbus A-321.

"Before the moment of the disappearance of the aircraft from radar screens, sounds are recorded which are not characteristic of a normal flight," Interfax quoted an unnamed security source in Cairo as saying.

A team of investigators led by Egypt and aided by experts from Russia, Airbus and Ireland visited the crash site on Tuesday as they try to find out the cause of the deadly crash.

Once investigations at the site finish, investigators are expected to focus on analysing the black box recorders, which are reportedly in good condition and could bring officials closer to finding out how the jet came crashing down.

On Tuesday, a US official told NBC News that the US intelligence community believed that it could have been some kind of explosion on the plane itself, either a fuel tank or a bomb.

The same satellite imagery ruled out a surface-to-air missile attack, the news channel reported.

Speculation of a possible bomb on board has continued, with Russian officials saying the plane broke up in midair.

Once investigations at the site finish, investigators are expected to focus on analysing the black box recorders [The Associated Press]

But Egyptian civil aviation officials have said there were no facts to substantiate assertions by Russian officials. Though officials have confirmed that no distress call was received, suggesting a sudden break-up to many experts.

Kogalymavia, a small airline that operated the flight under the name Metrojet, said on Monday that the disaster was most likely caused by a midair "impact" and that the plane had no technical problems.

Its announcement followed Egyptian and Russian authorities categorically ruling out claims from an affiliate of the Islamic State of Iraq and the Levant (ISIL) group that members of the Sinai-based group had downed the plane with a rocket.

Egyptian President Abdel Fattah el-Sisi said any rocket claims by ISIL were nonsense.

"When there is propaganda that it crashed because of ISIS, this is one way to damage the stability and security of Egypt and the image of Egypt," he told the BB, using a different acronym for ISIL.

The bodies of more victims arrived in Saint Petersburg early on Tuesday. A third plane is expected to arrive in the city later.

"We will do this work every day until all the dead and their belongings have been brought back," the deputy head of Russia's Civil Protection Agency, Vladimir Stepanov, told the Itar-Tass news agency.

The bodies of more victims arrived in Saint Petersburg early on Tuesday [AP Photo/Pavel Golovkin]

Source: Al Jazeera And DPA