Egypt's foreign ministry exchanged condolences with France on Thursday over what it called the "fall" of an EgyptAir flight carrying 66 people from Paris to Cairo.
The statement was the first official admission that those on board were likely to have died.
The plane was carrying people from multiple nationalities including 30 Egyptians and 15 French nationals. The flight was three children, including two babies.
Egypt's foreign ministry said in its statement that the two countries had agreed to cooperate closely in investigating the causes of the incident.