"The Kremlin and President Putin express deep condolences over the crash of the Egyptian plane," Peskov told reporters on Thursday, the Tass news agency reported.
"Now the circumstances of this crash are being investigated, various reports are coming, there is no full picture," he added.
Earlier in the day, Egyptian Prime Minister Sherif Ismail did not rule out that a terrorist attack might have been carried out onboard the EgyptAir A320 jet.
"We cannot exclude anything at this time or confirm anything. All the search operations must be concluded so we can know the cause,” he said.
The A320 plane of EgyptAir airline en route from Paris to Cairo disappeared from radars some 280 kilometers from the Egyptian coast early on Thursday. There were 66 people onboard from 12 countries - 56 passengers, including three children, and ten crew members.
Later, Greek authorities said the captain of a merchant ship had reported a "flame in the sky" some 130 nautical miles south of the Karpathos island.