Watchdog: Nuclear powers shrinking, modernizing arsenals

STOCKHOLM (AP) — The global number of nuclear warheads dropped last year, though none of the nine nuclear powers showed any signs of giving up their atomic weapons, an arms watchdog said Monday.

North Korea is believed to have built up to 10 warheads, but it remains unclear whether the reclusive communist country has produced or deployed any operational weapons, SIPRI said.

"North Korea claims to have designed and built a nuclear warhead that is sufficiently compact and robust for delivery by a ballistic missile," the report said.