White House Deputy National Security Adviser Tony Blinken says that it is too early to tell whether foul play was a factor in the disappearance of a Malaysia Airlines flight.

Blinken said Sunday that the U.S. was looking into reports that two passengers were using stolen passports, but investigators had reached no conclusions. He said it was premature to speculate whether the passengers had a role in the Boeing 777’s disappearance.

Blinken also said U.S. investigators from the FBI, the National Transportation Safety Board and the Federal Aviation Administration are heading to Asia to assist in the investigation.

The plane carrying 239 people lost contact with ground controllers somewhere between Malaysia and Vietnam after leaving Kuala Lumpur early Saturday morning enroute to Beijing.

Blinken appeared Sunday on CNN.

(AP)