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Nuclear-armed North Korea's testing of long-range missiles that could possibly reach US soil has kindled debate in Japan and South Korea about developing their own nuclear deterrent, prompting fears of a North East Asian arms race.
In the event of all-out war with North Korea, would US President Donald Trump risk American cities being targeted to protect traditional allies in Seoul and Tokyo?
That is the question causing jitters in South Korea and in Japan, where the topic of deploying or developing atomic weapons is especially taboo as the only country to have suffered a nuclear attack.
As a presidential candidate, Trump ruffled feathers when he suggested that Japan and South Korea should take more responsibility for their own defence.
And concerns that an "America First" policy might mean less military protection for allies many thousands of kilometres away have prompted some to suggest that they need to look after themselves.
In Japan, a series of missile launches from its unpredictable and nuclear-armed neighbour across the sea -- including one that crossed Japanese soil -- has caused some prominent figures to wonder aloud whether to reconsider the taboo.
Shigeru Ishiba, a hawkish former defence minister and veteran in Prime Minister Shinzo Abe's conservative LDP party, asked on a TV debate show on Wednesday: "Is it really ok not to talk about it any more?"
"Is it right to say that we want to be protected by US nuclear weapons but we don't want them on our soil?" asked the former minister, while acknowledging it was an "emotional" issue in pacifist Japan, still scarred by the obliteration of Hiroshima and Nagasaki in World War II.
Similar noises are emerging from South Korea, which is banned from building its own nuclear weapons under a 1974 atomic energy deal it signed with the US.
"As nuclear weapons are being churned out above our heads, we can't always rely on the US nuclear umbrella and extended deterrence," the mass-circulation Donga Ilbo newspaper said in an editorial Monday.
And there appears to be popular support, with a Moonhwa Daily poll last month showing nearly two thirds of respondents in favour of Seoul developing its own independent nuclear deterrent.
For decades, Japanese policy has been guided by the so- called "three principles": not producing, possessing or allowing nuclear weapons on Japanese territory.
And officials were quick to slap down Ishiba, with Chief Cabinet Secretary Yoshihide Suga saying: "Until now, we haven't discussed calling these three principles into question and we are not planning to do so."
South Korea has a similar official position, with Foreign Minister Kang Kyung-Wha stressing Seoul is still sticking to its commitment to the Non-Proliferation Treaty.