Former U.S. ambassador to the United Nations, John Bolton, had warned in the past that Syria and Iran could provide a "safe haven" in their territory for nuclear facilities built with equipment smuggled from North Korea.

In an article published in the Wall Street Journal on August 31, Bolton wrote that, "We know that both Iran and Syria have long cooperated with North Korea on ballistic missile programs, and the prospect of cooperation on nuclear matters is not far-fetched."

"Whether and to what extent Iran, Syria or others might be 'safe havens' for North Korea's nuclear weapons development, or may have already participated with or benefited from it, must be made clear," he added.