The A-321 airliner crashed over the Sinai Peninsula 23 minutes after takeoff. The Russian Embassy in Cairo said all 217 passengers and seven crew members on board were killed.
"The initial reports represent tremendous tragedy, loss, and we extend our condolences to the families and all those concerned," Kerry said on his visit to the Central Asian republic of Kyrgyzstan.
Egypt's Ministry of Civil Aviation was cited by media as saying a flight data recorder was found at the crash site.
Russian Transport Minister Maxim Sokolov said the causes of the catastrophe would be determined after an international probe with Russian participation is conducted. He said the Airbus had an airworthiness certificate.
Russian Prime Minister Dmitry Medvedev expressed his condolences and pledged a thorough investigation into the crash.
