A high-ranking North Korean defector told a US congressional hearing today that a pre-emptive US military strike on the country would trigger automatic retaliation, with the North unleashing artillery and short-range missile fire on South Korea.
The testimony from Thae Yong Ho, former deputy chief of mission at the North Korean Embassy in London, underscored the high risk in using military force against North Korea.
The Trump Administration has said this is among its options in stopping leader Kim Jong Un from perfecting a nuclear-tipped missile that could strike the United States.
Thae, the highest-level North Korean defector in two decades, appeared to confirm what has long been suspected but rarely articulated by US officials - that even a selective American strike could rain a potentially devastating North Korean military response on the South Korean capital and its area, about 40km south of the heavily militarised frontier.
Thae, who is making his first visit to Washington since his defection last year, said the US and allied South Korea would win a war after a preventive military strike on the North, but there would be a "human sacrifice" inflicted on the South from the "tens of thousands" of artillery guns and short-range missiles the North has at the frontier.
"North Korean officers are trained to press their button without any further instructions from the general command if anything happens on their side," Thae told the House Foreign Affairs Committee, referring to a US bombing or military strike.
"We have to remember that tens of millions of South Korean population are living 70 to 80km away from this military demarcation line."
He urged Washington to use "soft power" instead - enforcing sanctions and disseminating information challenging North Korean propaganda to turn people against Kim's authoritarian government.
He also contended that if China allowed an "exit route" for North Korean defectors without fear of forcible repatriation there would be a "massive exodus" to the South that would cause the collapse of the North Korean system.
North Korea has called Thae "human scum" and accused him of embezzling government money and committing other crimes.
Thae's comments come ahead of US President Donald Trump's five-nation trip to Asia that will include a stop in South Korea. The US Administration says it seeks a diplomatic solution to the nuclear standoff but "all options" are on the table.
Trump has threatened the total destruction of North Korea if the US is forced to defend itself or its allies.
A Congressional Research Service report published last week said that conservative estimates anticipate that in the first hours of a conflict, North Korean artillery situated along the frontier could cause tens of thousands of casualties in South Korea, where at least 100,000 and possibly as many as 500,000 Americans live - including nearly 30,000 US troops.
It said a protracted conflict, particularly one in which North Korea uses its nuclear, biological or chemical weapons, could cause enormous casualties on a greater scale.
Some analysts contend the risk of Kim acquiring a nuclear weapon capable of targeting the US homeland is greater than the risks associated with the outbreak of a regional war, the report said.