Egypt and Russia yesterday appeared to back away from their assertions that a Russian passenger jet crashed in the Sinai desert because of a technical fault, as it was revealed the plane broke up in the air and officials conceded it could had been brought down by a bomb on board. In the hours after the Airbus A321 crashed on Saturday - killing all 224 aboard and spreading debris and bodies over miles - both governments were quick to say the airliner appeared to be the victim of mechanical failure.But by last night Abdel Fattah al-Sisi, Egypt's President, was speaking more cautiously, saying it was too soon to tell the cause.Islamic State has claimed credit for destroying the aircraft, saying it was revenge for Russia's intervention in Syria.While experts believe it was flying too high to be hit by an IS missile, an Egyptian official told The Daily Telegraph it was possible the plane was brought down by an explosive planted on board.The official said a mechanical failure was still thought to be the most likely explanation but it was too early to draw firm conclusions. He said the pilot had not issued any distress call, suggesting the aircraft suffered a sudden calamity.Viktor Sorochenko, a Russian aviation official who inspected the crash site, said the Kogalymavia-operated flight "broke up in the air" which was why the debris was spread over 20sq km."Disintegration of the fuselage took place in the air, and the fragments are scattered around a large area," he said.Investigators have begun examining both black boxes.A grainy cellphone video circulated online purports to show the moment the airliner exploded, before hurtling down to earth, but its origins are unclear.However, it appeared to chime with eyewitnesses who said the plane fell flaming from the sky.Yves Trotignon, a former French intelligence agent, noted that the IS claim of responsibility was vague. "The statement does not say they shot it down, but that they destroyed it," he told Le Parisien. "You could imagine explosives on board, or sabotage."Terrorism experts said IS had never claimed an attack it did not carry out. Mathieu Guidère, professor of Islamic studies at the University of Toulouse, said IS "is very well established in the Sinai, has infiltrated almost all organisations and infrastructure, so it is possible a fighter sabotaged the plane at the airport before it took off, or placed a device on board". ..