North Korea war could 'kill 10,000 US troops within days'

A war with North Korea could result in 10,000 American combat-related casualties in the first few days alone, say US military planners.

A classified military exercise last week, attended by Army chief of staff General Mark Milley and head of Special Operations Command General Tony Thomas, tested hypothetical scenarios of how US troops would mobilise and strike if ordered to into a potential war, reported the New York Times.

The "tabletop exercise", held in Hawaii, thrashed out challenges that could hamper a US assault on North Korea's sizeable military.

It determined that US casualties could be amplified by the Pentagon's limited ability to evacuate injured troops daily, and by the possibility that Pyongyang could retaliate with chemical weapons.

Civilian casualties would far outweigh the initial toll on US troops, and potentially reach hundreds of thousands, commanders were told.

While the US stations about 28,500 troops in South Korea, its capital Seoul, a city of about 24 million, lies within range of the formidable firepower of North Korea's artillery.

The potential human costs of any war were so high that, at one point in the exercise, General Milley remarked "the brutality of this will be beyond the experience of any living soldier" said the Times.

Pentagon chiefs cautioned that the planning session did not mean a decision has been made to go to war with the intention of curbing Pyongyang's nuclear ambitions.

The unpredictable situation has sparked fears among US military leaders of a "ladder of escalation". Photo / AP

After a diplomatic detente with South Korea during the Winter Olympics, Pyongyang indicated it was willing to open up dialogue with Washington.

President Trump's response that "we want to talk also" but "only under the right conditions" has created a glimmer of hope of a diplomatic solution. But America's insistence that denuclearisation must be on the table remains a sticking point.

A war with North Korea would be catastrophic.

Defence Secretary Jim Mattis

The unpredictable situation has sparked fears among US military leaders of a "ladder of escalation", where a stray incident could cause a military crisis to spiral out of control.

Defence Secretary Jim Mattis has said a war with North Korea would be "catastrophic" but has reportedly ordered top Pentagon officials to be ready for any possible military action.

Among plans discussed was the redeployment of surveillance aircraft from the Middle East and Africa to the Pacific and how US forces in Japan and South Korea would be involved.