In Washington, a Bush administration official says Pyongyang is working on new ballistic missile systems designed to deliver nuclear warheads.
Speaking on condition of anonymity, the official also said Friday that the North is sharing related technology with Iran, which Washington claims carries out missile tests on North Korea's behalf.
According to the official, the missile program is based on Russian technology and has been conducted with help from Russian scientists.
The official's remarks come as British military magazine, Jane's Defence Weekly, said earlier this week that North Korea was developing two new ballistic missile systems that "appreciably expand the ballistic-missile threat.