The United States say it can’t rule out the possibility of terrorism in the crash of a Russian plane in Egypt’s Sinai Peninsula.

White House spokesman Josh Earnest says the U.S. hasn’t determined what brought down the Metrojet flight last Saturday, killing all 224 people onboard.

Earnest says he can’t discuss what U.S. intelligence officials have learned so far.

He also says the administration is reviewing what steps it can take to enhance security on commercial flights to the United States from certain countries.

Islamic State militants are taking responsibility for the crash — as a response to Moscow’s recent military intervention in Syria against the extremist group. But IS hasn’t provided any evidence to support that claim.

(AP)