The United States moved yesterday to take the heat out of the North Korean crisis by stating that United Nations sanctions against Kim Jong Il's isolated nation were not an option at present.

The remarks by the deputy US ambassador to the UN, Richard Williamson, came after Pyongyang was referred to the UN Security Council for breaking non-proliferation agreements.

Washington is eager to play down the North Korean issue to allow it to complete preparations for a military invasion of Iraq. Mr Williamson stressed that the Bush administration wants a diplomatic solution to its dispute with North Korea.

His remarks followed a fresh burst of bellicose warnings from North Korea after the UN's nuclear monitoring body, the International Atomic Energy Agency, referred the issue to the Security Council – a process that could lead to the imposition of sanctions.

American intelligence believes Pyongyang is within months of producing material for several atomic weapons. The UN referral, though expected, further heightened tension in the region.

Matters were further complicated by a crime scandal in South Korea that could hardly have been worse timed. Anti-American sentiment in the country seemed likely to grow yesterday after a US military court found an American soldier guilty of charges including sodomy and aggravated assault against an off-duty South Korean soldier. The court martial sentenced Sergeant Leng Sok to 30 years in a military jail in Kansas.

It is not clear whether this pointedly tough penalty will prevent further controversy over the 37,000 US troops stationed in South Korea, long a source of tension. And the case may have further to run: two other American soldiers are under investigation for the assault, and the convicted sergeant has the right of appeal.

Reports said the sergeant's victim was one of 4,600 South Koreans serving with the US military in Katusa (the Korean Augmentation to the United States Army). The uneasy relationship between the US and South Korea has been one of many complicating factors for Washington in the current stand-off with the North.

Last year, there was an upsurge of anti-US sentiment after two teenage girls were run down and killed by a US armoured vehicle. Two American soldiers who were in the vehicle were acquitted by a US military panel, prompting angry demands for a revision of the treaty governing the US military presence.

In the latest case, the decision to let the US Army try the case was taken by the South Korean authorities.

The public's anger over the girls' deaths fused with larger unease among South Koreans over American tactics for dealing with the North.

American reprisals against Pyongyang for its nuclear-related activities, and President George Bush's "axis of evil" remarks, have met strong criticism in South Korea.

Nerves were further frayed this week when US intelligence officials told Congress that the North Koreans have an untested ballistic missile capable of hitting the US. According to the director of the US Defence Intelligence Agency, Vice-Admiral Lowell Jacoby, it is a three-stage version of North Korea's Taepo Dong 2. US officials have talked before of a missile capable of reaching America's west coast, but they now indicate that its range could be even greater.