Egypt’s Prime Minister Sherif Ismail said it was too early to rule out any explanation for the incident, including terrorism.

“Search operations are ongoing at this time for the airplane in the area where it is believed to have lost contact,” Ismail told reporters at Cairo airport, according to Reuters.

Asked if he could rule out that terrorists were behind the incident, he said said: “We cannot exclude anything at this time or confirm anything. All the search operations must be concluded so we can know the cause.”