"What we know is that an individual of Iranian-American descent was involved in a plot to assassinate the ambassador to the United States from Saudi Arabia," Obama said. "And we also know that he had direct links, was paid by and directed by individuals in the Iranian government. Now those facts are there for all to see."

He praised the "outstanding" U.S. intelligence work that helped thwart the plot that he said would also have killed innocent civilians.

"We would not be bringing forward a case unless we knew exactly how to support all the allegations that are contained in the indictment," he said.