Addressing a hastily-convened national security meeting, Moon said the North's latest launch of an intercontinental ballistic missile (ICBM), which splashed down in waters near Japan, was a "reckless provocation" that would raise already elevated tensions to critical levels.
"The situation could get out of control if the North completes the development of ballistic missiles that can fly to a different continent," Moon said.
"We have to prevent such a scenario where the North may miscalculate the situation and threaten us with nuclear weapons, or the US may consider a pre-emptive strike (against the North)," he added.
There are particular concerns in Seoul that US President Donald Trump might consider some sort of military action against the North that could escalate into all-out war -- a horrifying scenario for the South which would bear the immediate brunt of any conflict.
The South's capital Seoul is home to 10 million people and only about 50 kilometres from the border, within range of Pyongyang's artillery.
One study by the Nautilus think-tank in California estimated around 65,000 civilians would die in Seoul alone on the first day of a conventional North Korean attack.
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