By Ju-min Park
YEONCHEON, South Korea (Reuters) - As North Korea prepares a third nuclear test, South Korean soldiers on the world's most heavily armed border now have orders to shoot back immediately if they come under attack, a move that risks escalating any small-scale conflict.
Stung by criticism three years ago of the time it took South Korean artillery to respond to a burst of shelling from the North, Seoul's Defence Ministry has relaxed rules that required officials at its command centre to sanction a response.
"We will respond immediately to any enemy provocation," said Captain Kim Sang-min, a 29-year old company commander at the "Invincible Typhoon" unit that is stationed just 800 meters from the demarcation line that separates the two countries which remain technically at war.
The Defence Ministry in Seoul declined to specify the remit of the new orders, citing national security concerns, although Defence Minister Kim Kwan-jin has urged soldiers over the past year to "punish automatically ... until the enemy surrenders".
That is an unlikely prospect in a country whose military is kept in check by the United States, its main diplomatic ally, but the prospect of conscripts firing back has raised concerns that a small incident could escalate.
The United States heads the joint command that is in charge of the two countries' military response to any North Korean military action.
Both the United States and the South have kept a lid on activities that could risk a further escalation, even when the South has been attacked - as it was in 2010 when the North shelled a South Korean island, killing two civilians.
The South fired back but was criticized by the public for the length of time it took to respond.
North Korea shelled the island at 2.34 pm local time according to official records in Seoul and South Korea started firing back around 15 minutes later, though the time is disputed and the official account has been questioned by the public. The South's defence chief was sacked for the tardy response.
The North is also blamed for the sinking of a South Korean naval vessel in the same year. Forty-six sailors were killed.
There were no reported casualties from the South's response to the fire from the North's artillery batteries, which dropped 170 rounds on Yeongpyeong island, some 80 km (50 miles) from the coast of South Korea and just 12 km (7 miles) off North Korea.
Tensions are once again climbing on the Korean peninsula, with Pyongyang stepping up its shrill rhetoric and saying it will stage a third nuclear test soon as well as unspecified "stronger" measures.
Captain Kim and his unit patrol the ice-caked minefields and barbed-wire fences of a border that is just 65 km (40 miles) from the bustling modern South Korean capital, home to 10 million people.
The silence is broken by wild boars or magpies in the sky and occasionally by the sound of North Korean small arms or artillery from the million strong army over the border.
South Korea's young conscripts, many of whom come from comfortable homes in affluent cities, say they are struck by the reality of the Korean peninsula's cold war when they are called up to serve their 21 months of military service.
"Before joining the military, I didn't feel that my country was still at war and I wasn't worried," said Shin Dong-joon, a 23-year-old conscript with the Invincible Typhoons who has spent six months on the border since being called up.
"Now it is more real serving on the northern-most border of the Republic of Korea and seeing the land that is North Korea for myself."
The Republic of Korea is the official name of South Korea.
Within the military, there is anger over the South's quiescence in the face of repeated attacks by the North - dubbed "provocations" by government officials in Seoul.
After the North's 2010 attack on Yeongpyeong island, South Korean TV aired footage of artillery shells raining down on civilian settlements - images that are burnt into the memory of one officer, an army veteran.
"People on the island were rats in a trap," he recalls.
"Our response manual has been strengthened so it's clearer that we should fire back," added the officer, who declined to be identified as he was not authorized to speak to the media.
(Reporting by Ju-min Park; Editing by David Chance and Mark Bendeich)