U.S. Admiral Mike Mullen says North Korea is a growing danger that must be stopped.
Mullen, the chairman of the Joint Chiefs of Staff, however, cautioned that any reaction to North Korea must be proportional and not escalate the conflict.
Speaking in Tokyo, Mullen also accused China of not doing enough even though it has more influence over North Korea than any other government.
Meanwhile, North Korea has released a report defending last month's deadly attack on a South Korean island.
It accuses Seoul and Washington of "persistently escalating tension" in disputed seas off its west coast.
compiled from agency reports