WASHINGTON - US-bound parcels at Cairo airport contained no explosives, CBS News quoted an Egyptian Interior Ministry source as saying on Tuesday.CBS News earlier reported that Egyptian officials were investigating the possibility that packages being shipped by express mail service company DHL to the United States contained explosives. Egyptian security forces have been on heightened alert since a terrorist attack caused a Russian passenger plane to crash last month killing all 224 people on board. A terrorist group affiliated to Islamic State in Egypt claimed responsibility for the downing the plane shortly after the incident. Islamic State's official magazine carried a photo last week of a Schweppes soft drink can it said was used to make an improvised bomb that brought down the Russian airliner over Egypt's Sinai Peninsula.The photo showed a can of Schweppes Gold soft drink and what appeared to be a detonator and switch on a blue background, three simple components that if genuine are likely to cause concern for airline safety officials worldwide."The divided Crusaders of the East and West thought themselves safe in their jets as they cowardly bombarded the Muslims of the Caliphate," the English language Dabiq magazine said in reference to Russia and the West. "And so revenge was exacted upon those who felt safe in the cockpits."