What will Kim do next? Sixth nuclear test seen critical for North Korea

North Korean leader Kim Jong Un inspects the intercontinental ballistic missile Hwasong-14 in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang July 5, 2017. KCNA/via REUTERS

SEOUL/WASHINGTON (Reuters) - North Korea says it has developed intercontinental missiles capable of targeting any place in the United States.

Now comes the hard part of fulfilling the declared goal of its leader Kim Jong Un: perfecting a nuclear device small and light enough to fit on the missile without affecting its range as well as making it capable of surviving re-entry into the earth's atmosphere.