SEOUL (South Korea) • The stand-off over North Korea's nuclear programme has long been shaped by the view that the United States has no viable military option to destroy it. Any attempt to do so, many say, would provoke a brutal counter-attack against South Korea too bloody and damaging to risk.

The stakes are higher now for the US but the military options are more grim than ever. Analysts say there are many ways and reasons for each side to escalate the fighting once it begins. Stopping it would be much more difficult.

OPENING SALVOS

North and South Korea, separated by the world's most heavily armed border, have had more than half a century to prepare for a resumption of the war that was suspended in 1953. While the North's weaponry is less advanced, the South suffers a distinct geographical disadvantage: Nearly half of its population lives within 80.5km of the Demilitarised Zone, including the 10 million people in Seoul, its capital.

North Korea has positioned as many as 8,000 artillery cannon and rocket launchers on its side of the Demilitarised Zone, analysts say, an arsenal capable of raining up to 300,000 rounds on the South in the first hour of a counter-attack. That means it can inflict tremendous damage without resorting to weapons of mass destruction.

Most analysts expect the North would escalate quickly if attacked, to inflict as much damage as possible in case the US and South Korea were preparing an invasion.

"North Korea knows it is the end game and will not go down without a fight," said Dr Jeffrey W. Hornung of Rand Corporation, adding: "I think it is going to be a barrage."

A study published by the Nautilus Institute for Security and Sustainability in 2012 concluded that the initial hours of an artillery barrage by the North focused on military targets would result in nearly 3,000 fatalities, while one targeting civilians would kill nearly 30,000 people. The North could compound the damage by also firing ballistic missiles at Seoul.

THE DEFENCE

US and South Korean forces could be put on alert and bracing themselves for retaliation before any attempt to knock out North Korea's nuclear programme. But there is little they can do to defend Seoul against a barrage of artillery. The South can intercept some ballistic missiles, with the recently installed Terminal High Altitude Area Defence system, as well as Patriot and Hawk systems. But it does not have anything like Israel's Iron Dome that can destroy incoming artillery shells and rockets, which fly at lower altitudes.

Instead, South Korean and American troops would employ traditional "counter-battery" tactics - using radar and other techniques to determine the location of the North's guns when they are moved out of their bunkers and fired, and then using rockets and air strikes to knock them out. What makes the situation so dangerous is how easy it would be for either side to take action that leads the other to conclude an all-out war is imminent and escalate the battle.

CIVILIAN PREPARATION

All things considered, analysts say, it could take American and South Korean forces three to four days to overwhelm North Korea's artillery. How much damage North Korea inflicts in that time depends in part on South Korea's ability to get people to safety quickly.

As more of the North's guns are destroyed and people take cover, the casualty rate would fall with each hour.

The Nautilus Institute study projects 60,000 fatalities in the first full day of a surprise artillery attack on military targets around Seoul, the majority in the first three hours.

Casualty estimates for an attack on the civilian population are much higher, with some studies projecting more than 300,000 dead in the opening days.

The Seoul metropolitan government says there are nearly 3,300 bomb shelters in the city, enough to accommodate all 10 million of its residents. But critics say the local authorities are unprepared for the chaos an artillery attack would cause and that the public is nonchalant about the prospect of war.

NEW YORK TIMES