North Korea's nuclear ambitions dominated South Korea's presidential election campaign on Monday, with the two main candidates differing sharply over how to handle the secretive state.

Roh Moo-hyun of the ruling Millennium Democratic Party called the election a choice between "war or peace".

Mr Lee wants to suspend aid to North Korea

He accused his conservative opponent Lee Hoi-chang of wanting to cut aid to the North and end North-South dialogue.

But Mr Lee, candidate for the Grand National Party (GNP), said the government's so-called "Sunshine policy" of engaging with North Korea had made too many concessions and gained little in return.

"We cannot entrust the country to a person who says we must keep on giving cash to North Korea while our cash comes back as nuclear programmes threatening the lives of our people," Mr Lee said.

The two men appear to be neck and neck ahead of Thursday's poll.

Analysts said that arguments over North Korea and a sudden wave of anti-American sentiment could tip the race either way.

North Korea alarmed many voters last week by threatening to resume a nuclear programme which was frozen under a 1994 deal with the United States, and which could be used to produce nuclear weapons.

According to the US, North Korea has also admitted to a fresh nuclear weapons programme, which was also banned under the 1994 agreement.

Public anger

The poll also comes amid growing anti-American sentiment over the acquittal of two US soldiers accused of negligent homicide in a road accident which killed two teenage girls in June.

There was a huge anti-US protest in Seoul on Saturday

On Sunday night a senior US officer was attacked by three men carrying a knife who swore at him and told him that US forces should leave South Korea.

Lieutenant Colonel Steven Boylan, who was unarmed, was treated in hospital for minor injuries after he was attacked as he left a US army base at Yongsan.

Last month two US soldiers were cleared in a US military court over the deaths of the two girls, who were crushed by a US military vehicle.

The case has sparked widespread anti-American feeling in South Korea, which hosts 37,000 US troops under a defence agreement dating to the 1950-53 Korean War.

The government has opened talks with US officials to improve the code governing the legal status of the US troops. The US can currently refused to have accused soldiers put on trial in South Korean courts.

Mr Lee and Mr Roh have both criticised the verdict in the case of the two soldiers.