Authorities are refusing to rule out that an EgyptAir passenger jet that crashed into the Mediterranean Sea early Thursday morning was brought down by an act of terrorism.

Egypt’s foreign ministry said on Thursday evening that debris found near the Greek island of Karpathos, where Greece’s military radar lost contact with the plane flying from Paris to Cairo, was from the missing aircraft, according to a person close to EgyptAir. However, doubt was subsequently cast on that claim after Athanasios Binis, head of Greece’s air safety authority, told AFP that the debris was not from an aircraft.

US intelligence services are helping French and Egyptians authorities analyse the list of 56 passengers for possible terrorist connections. However, Josh Earnest, White House spokesman, said: “It is too early to definitively say what has caused this disaster.”