With North Korea seemingly intent on going ahead with its planned rocket launch, the international community must decide how it can punish a country that has proved largely impervious to past sanctions.

The options open to the United States and its allies are limited by several factors, not least that individually and collectively they have already exercised most of what little leverage they have over the isolated state.

On a truly multilateral level -- meaning UN sanctions -- they are wholly dependent on the stance taken by veto-wielding China which, in the past, has proved resistant to the tougher measures demanded by other nations.

"China sets the maximum response level in the Security Council when it comes to North Korea," said a senior South Korean government official. "So the existing list of UN sanctions on the North is essentially China's list."

After Pyongyang's last failed rocket launch in April, the United States, European Union, South Korea and Japan put forward 40 state companies they wanted added to a UN blacklist of North Korean firms.

China consented to only three, although it also agreed to a Security Council statement warning of further action if the North made a new attempt.

"After that threat the council should now act, but much will depend if China is ready to do something," a senior UN diplomat told AFP.

"In reality, the discussions about action will be between the United States and China. The US will have to convince the Chinese to take new sanctions," the diplomat said.

Washington and its allies insist the launch is a disguised ballistic missile test that violates UN resolutions triggered by Pyongyang's two nuclear tests in 2006 and 2009.

In 2006 the Security Council imposed an embargo on arms and material for ballistic missiles and weapons of mass destruction. It also banned exports of luxury goods and named individuals and companies to be subject to a global assets freeze and travel ban.

In 2009, it imposed a ban on North Korea's weapons exports and ordered all countries to search suspect shipments.

China publicly joined the rest of the international community in urging North Korea to call off this month's launch attempt, but it remains unclear how much pressure it exerted behind the scenes.

As North Korea's sole major ally and its biggest trade partner and aid provider, Beijing has more leverage than most.

But analysts like Wang Dong, director of the Centre for Northeast Asian Strategic Studies at Peking University, say its influence can be over-stated.

"If you think that, because I give you economic aid, and I give you energy, then I can bring you to your knees, I can pressure you to listen to me, you become my puppet, it would be an illusion," Wang said.

Although genuinely concerned that a rocket launch could unsettle the region, Wang said Beijing was unlikely to agree to any significant expansion or tightening of sanctions to penalise Pyongyang.

"Generally speaking, China refrains from using coercive measures in trying to bring others to terms with what it wants," he said, adding that it would likely maintain that stance "unless North Korea does something really provocative".

What would seriously rattle China -- and Russia -- would be another nuclear test by the North, which some see as a distinct possibility given that its two previous tests both followed long-range missile launches.

A successful launch this time would mark a major advance in the North's bid to mate an intercontinental ballistic missile (ICBM) capability with its nuclear weapons program.

As such, it would pose a direct threat to US national security.

Bruce Klingner, a former CIA officer and senior research fellow at the Heritage Foundation, a right-leaning US think tank, said there was room to tighten the screws on North Korea.

"There could be a closing of some of the loopholes in the existing sanctions," Klingner said, citing articles of the UN charter that allow for enforcement of UN resolutions by military means.

"But so far China has always been resistant," Klingner said. "That's why we've had the fiascos of the US Navy chasing a slow-moving North Korean freighter in the Western Pacific even though we suspect it's carrying prohibited items."

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