WASHINGTON (Reuters) — The United States expects backing from China, South Korea and Japan in a push for new sanctions after North Korea tested a nuclear weapon, but it is unclear whether the three key Asian states will go as far on penalties as Washington might think necessary.“If there is no reaction by the international community, this could mean end to the nuclear Non-proliferation Treaty and it would set a bad precedent for other countries, like Iran,” a senior Republican US congressional aide said, referring to the current stand-off between major powers and Tehran over Iran’s nuclear programme.

Still, he worried about the United States and North Korea “playing a game of chicken” and said the nuclear issue “is on a train to the cliff and nobody can stop it.”

The United States has had sanctions on the isolated and economically devastated communist state since after the 1950-1953 Korean War. Even before yesterday’s test, US officials had discussed re-imposing trade prohibitions lifted by former President Bill Clinton when Pyongyang agreed to a missile moratorium that was recently abandoned.

Options beyond that are limited, although not without potential impact. American firms do little business with the North and so major new post-nuclear test pressure would have to come from Northeast Asian neighbours who are Pyongyang’s main trading partners, especially China, its main source of fuel and food aid.

“If they do test, the strategic situation changes fundamentally and the consequences need to be swift and dire,” one senior US official told Reuters last week.

South Korea and China — fearing instability on the Korean peninsula — previously cautioned against backing the North into a corner, although Japan supports a hard line toward the North. All expressed outrage about yesterday’s test.

One US proposal would seek to tighten a UN Security Council resolution adopted after the North test-fired a series of missiles last July in defiance of international pleadings. That would aim to put greater pressure on countries to crack down on banks and businesses deemed to be aiding the North’s weapons of mass destruction programs and ensure close scrutiny of North Korean cargo ships at foreign ports, officials said.

Another idea would have countries stage military exercises in the waters near North Korea under the auspices of the Proliferation Security Initiative, which aims to encourage member countries to share intelligence and train to interdict weapons from the North, Iran and other states of concern.

The exercises would not be called a blockade but could have a similar effect, by keeping Pyongyang from exporting missiles or fissile material, officials said.

White House spokesman Tony Snow said early yesterday, however, the United States is not putting a blockade in place and the Navy is not intercepting North Korean shipping.

Congressional sources said one indirect penalty would be excluding North Korea’s Kaesong industrial project from a US-South Korea free trade agreement now under negotiation.

South Korean businesses want to import into the United States without tariffs goods made in Kaesong, but Congress almost certainly will not go along because of Pyongyang’s poor labour and human rights record, the sources said.

President George W. Bush has long taken a hard line against Pyongyang. Critics doubt he abandoned visions of changing the political system in the North and say he never gave US negotiators in the six-party talks flexibility to get a deal under which the North would trade its nuclear weapons for political and economic benefits.

Days before the nuclear test Sen. Joseph Biden of Delaware, the Senate Foreign Relations Committee’s top Democrat, pleaded with Bush to reconsider his refusal to permit direct US-North Korean talks.

This would not “reward bad behaviour” but would enable Washington to make clear what Pyongyang could achieve by not testing and by ending its nuclear weapons programme, Biden said in a letter.

But there has been no indication the administration might consider holding such talks.