By Charles Scanlon BBC correspondent, Seoul

A company of American soldiers forms up outside their barracks, the advance guard of 37,000 US troops based in South Korea.

They are deliberately placed in the front line to deter a Communist attack.

Anti-US protests are becoming a regular event

But these are awkward times for the US military in Korea. While the North looks threatening, the South is an increasingly reluctant host.

Nationalist feelings are growing in South Korea, even among Korean troops that serve alongside the Americans. US officers talk about bruised feelings following a series of mass anti-American demonstrations.

"I think there's a heightened awareness that we probably just need to talk about - the conditions that caused that anti-American sentiment," says Lieutenant-Colonel Matt Margotta, who commands the joint battalion at Camp Bonifas.

"I mean there are certain differences between the United States and the Republic of Korea.

"There's differences in our culture, differences in our beliefs, and I think the more time that we spend talking about that and both sides understanding each other, the better we'll get along," he said.

New president

At the truce village of Panmunjom where the Koreas meet, the standoff continues. South and North Korean troops try to stare each other down across the military demarcation line that runs through the village.

President-elect Roh says he will not "kow tow" to the US

But there is little increase in tension despite the North's move in December to restart its nuclear programme.

For more half a century North Korea has been faced by a combined force of South Korean and American troops. It can only look with satisfaction at the growing rift between its old adversaries.

In December, South Koreans elected a president who is openly sceptical of US policy. Roh Moo-hyun sees himself as a mediator between Pyongyang and Washington rather than an instinctive American ally.

It's different seeing people that you're helping protect rally against you US serviceman

Rallies and candlelit vigils continue against the American military presence. They began after the acquittal last year of two US servicemen whose armoured vehicle crushed two Korean girls to death.

Even the latest James Bond movie has inspired protests. It portrays North Korea as an evil kingdom bent on world domination.

That is too much for Korean nationalists in the South who increasingly see the US as the real threat.

"I think they should stop showing 007," one man said. "They should stop disregarding Korean people."

Another man said: "The film portrays the North as the god of all evil. But we don't feel that way - they're Koreans like us."

Soldiers spat at

Scott Snyder of the US-funded Asia Foundation in Seoul said the message is getting through to Washington. Rising nationalism in the South can no longer be ignored.

"If the government and if the public decides that US troops are no longer needed, I think the US government and public will expect that they will be withdrawn because the American public does not see itself, or see the US, as an imperialist power," he said.

"If we're not wanted in a particular place, or the protection that those security forces provide is no longer perceived as needed, then indeed I think they will be withdrawn."

Out on the town near the US base in Seoul, soldiers are only welcome in certain bars and clubs. Some say they have been spat at and insulted on the street.

"It's different seeing people that you're helping protect rally against you," one US serviceman said. "It's a little hard to swallow at first. I didn't expect to see that."

Another said: "I figure it's probably because they've gone 50 years with the peace agreement and nothing's really happened.

"Maybe they think they don't need us here any more. But, from my point of view, I still see it and I still understand why we're here."

For young recruits who are told they are defending democracy, it can be an unsettling and perplexing experience.