New satellite images suggest North Korea is restarting its nuclear activity.
Joel Wit, a senior fellow at the U.S.-Korea Institute, says the country is back at work on a plutonium reactor.
"'In the most recent image that we have of the Nyongbyon nuclear facility, which is the main nuclear facility in North Korea, we think that North Korea is in the process of, or has begun, operation of a small reactor that is able to produce plutonium for nuclear weapons," Wit said.
Wit said the new revelation is not a surprise.
"This isn't a shock because in April, North Korea announced that it was basically going to restart this reactor, which had been shut down previously as a result of an international agreement," he explained.
The threat was one of the many declarations made to the United States and South Korea after the country faced tough international censure over its nuclear and rocket tests.
The restarted reactor was closed in 2007 under the terms of a disarmament agreement.