WASHINGTON (AP) — A U.S. official said Thursday that American intelligence authorities now believe a surface-to-air missile took down the Malaysian passenger plane as it flew over eastern Ukraine.

The official said the U.S. was still working to determine additional details about the crash, including who fired the missile and whether it came from the Russian or Ukraine side of the border. But the official said U.S. intelligence assessments suggest it is more likely pro-Russian separatists or the Russians rather than Ukrainian government forces shot down the plane.