"Deeply shocked by the Kogalymavia airline Airbus-321 liner catastrophe in the Sinai Peninsula…The circumstances of the incident will be thoroughly investigated," Medvedev wrote on his VKontakte social networking account.
The Russian prime minister added that the suspected death of all 217 passengers and seven Flight 9268 crew members en route from the Egyptian tourist resort of Sharm El-Sheikh to St. Petersburg was an "irreparable loss."
"A terrible tragedy claimed the lives of the people who were full of energy and plans," he said, pledging medical, psychological and other forms of help to those affected.
Russian Transport Minister Maxim Sokolov said the causes of the catastrophe would be determined after an international probe with Russian participation is conducted.
Sokolov said the Airbus, which disappeared from radar screens 23 minutes after take-off, had an airworthiness certificate.
Egypt's Ministry of Civil Aviation was cited by media as saying a flight data recorder was found at the crash site.