By Caroline Gluck BBC correspondent in Seoul

Street protests have widened in recent weeks, triggered by the recent controversial acquittal by a US military court of two American soldiers charged with negligent homicide in the deaths of two South Korean teenagers.

Young and old have joined the demonstrations

They were crushed to death by a US armoured vehicle on a training exercise on the outskirts of Seoul in June.

The outrage surrounding the case has resulted in the biggest shows of anti-American feeling in recent years.

Around 10,000 protesters have gathered in the streets around the American embassy in the capital, Seoul, in recent days, while other demonstrations have taken place around the country.

Holding memorial candles, demonstrators have shouted slogans calling for President Bush to apologise to the nation and for American troops to be punished.

Election factor

Hahm Sung-deuk, director of the Korea Presidential Studies Institute, said the issue had become a key factor in the election.

Restaurants and pubs are also taking a stand

"This issue became critical issue in presidential campaigning. People thought the current presidential candidate of the Grand National Party, Lee Hoi-chang, is too close to the United States," he said.

"In contrast, the presidential candidate, Roh Moo-hyun, of the New Millennium Party, is a little bit independent from the United States. So this issue may give an edge to the presidential candidate, Roh Moo-hyun," Mr Hahm said.

As the protests have spread, the two main presidential candidates have tried to capitalise on the public mood.

They are backing calls for revisions to the Status of Forces Agreement (Sofa), a legal code governing US troops in South Korea, which critics say is tilted in favour of the US.

Some protesters say the issue will influence how they vote.

"As a mother I feel the pain of (the dead girls') parents," said one woman.

"I think that whoever can resolve this issue should become president. Everyone thinks so."

Another woman noted: "In the past Korea kept quiet about these things. But now all the candidates are taking an interest. With so many protests going on, how can they ignore it?"

As the protests continue, many believe that Mr Roh, who has called for equality in the South Korean-US relationship, could benefit the most.

Unlike his conservative rival, he supports continued exchanges and aid to North Korea.

He has criticised President Bush's hard-line policy towards the Communist state.

Relationship risk

Protests overshadowed a US official's visit

Scott Sneider, from the US-based think-tank The Asia Foundation, believes that the street protests have been encouraged for political reasons and could seriously damage South Korea's relationship with the United States.

"Right now it's just a kind of erosion and corrosion that is leading to a loss of trust, but at the very least I think that both sides are going to have to step back and take a good hard look at the relationship," he said.

"The alliance has served both countries well for a long period of time but the kinds of sentiments that are being expressed - if they're not handled properly, and in particular if they lead to violence - I think could have a galvanising impact on American public opinion that would be quite dangerous."

South Korean public opinion has shown itself a force not to be ignored, and it is directly influencing foreign policy.

That could present more challenges - and difficulties - for whoever is elected president in managing the country's relationship with the United States in the years ahead.