North Korea Ups Activity at Nuke Site, Says South

North Korea is boosting "activities" at its Punggye-ri nuclear test site, South Korea says, though Seoul is keeping details classified. The South says it's "currently detecting a lot of activity in and around the Punggye-ri nuclear test site," and is tracking the situation as it ensures its own military readiness. Previous North Korean nuclear tests have used plutonium, but last month the country spoke of "a new form of a nuclear test"; experts say that statement could refer to uranium, reports CNN. On the other hand, Seoul says, the increased activity could just be a ruse.

It's possible "that North Korea may suddenly conduct a nuclear test" or "deceive us with what appears to be a nuclear test," says a South Korean defense spokesman. The North has suggested it had "something big" planned before April 30, the rep says, per Yonhap. The South's foreign minister called any test a "game changer," the BBC notes. The news comes as President Obama prepares to visit South Korea starting Friday, as part of a trip the North says seeks to "bring dark clouds of a nuclear arms race to hang over this unstable region." (More North Korea stories.)