Asia-Pacific allies and security partners of the United States are scrutinizing every move made by Washington as North Korea threatens to strike South Korea and launch missile attacks against American bases in Japan and the Western Pacific.

Surrounded by senior military officers, the North's mercurial young leader, Kim Jong Un, declared Saturday that his impoverished but nuclear-armed country was "entering the state of war" with South Korea. The day before, he announced that "the time has come to settle accounts with the U.S. imperialists in view of the prevailing situation."

The bellicose rhetoric from Pyongyang may turn out to be just its latest blackmail attempt to try to extract concessions from the U.S. and the international community, following North Korea's third nuclear weapons test in February and its successful launch in December of a long-range ballistic missile. But the crisis has reignited calls from conservative politicians and analysts in Seoul for South Korea to develop its own nuclear weapons and for the U.S. to reintroduce tactical nuclear arms into the South to deter North Korean aggression.