WASHINGTON -- Signs of growth in North Korea's nuclear program and the country's increasing isolation are renewing fears about Pyongyang's ability and need to smuggle weapons of mass destruction around the world, said U.S. and United Nations officials.

North Korea's arms trade has focused on Iran and Syria, countries Washington views as state sponsors of terrorism, as well as Libya. Officials say North Korean arms have also been sold to nations allied with the U.S., such as Egypt and Pakistan, and to the military regime in...