N.Korea Still Building Long-Range Missiles, U.S. Warns

North Korea is still trying to build intercontinental ballistic missiles tipped with a nuclear warhead, U.S. Defense Secretary Mark Esper has warned.

"Clearly they are trying to build long-range ballistic missiles with the ability to carry a nuclear warhead," he said. "So it's something we're watching very closely."

Esper was speaking at an international security forum hosted by the Center for Strategic and International Studies in Washington last week.

Asked how far the North has gotten in the development of a new strategic weapon it has threatened to build, he said, "They have an aggressive R&D program and test program, to say the least, and we monitor it very carefully and very closely."

But he added, "It still remains to be the case that we're pursuing a diplomatic initiative with them. We think the best way forward is through a political agreement." "At this point we need to get back to the negotiating table and really figure out the best way forward to denuclearize the peninsula," he said.

CNN quoted U.S. officials on Sunday as saying that recent satellite imagery shows vehicular activity at the Sanumdong missile research center near Pyongyang "that could potentially signal early preparations for a missile or missile engine test."

A large blue shipping container appeared, disappeared, and reappeared in images several times in January, and vehicular activity has been intermittent.

The "activities are consistent with what we've seen prior to other missile tests," said one senior U.S. official. But other officials said that "there is no indication of an imminent test launch," but added they still "cannot rule it out."

The Sanumdong missile research center is thought to be the North's key facility for the development of ICBMs.