Two decades of U.N. condemnations, threats, and sanctions have not stopped North Korea's nuclear ambitions. So, what does the Security Council have left to throw at Pyongyang?

The U.N. Security Council first called on North Korea to rein in its nuclear ambitions in 1993; more than a decade later, in 2006, it imposed its first round of sanctions to compel Pyongyang to freeze its nuclear and ballistic missile tests.

The U.N. pressure campaign -- punctuated by perennial bouts of nuclear diplomacy with Pyongyang -- has left Democratic and Republican administrations with little to show for their efforts. During the Obama administration, the Security Council has expanded the sanctions and threatened four times to impose additional penalties on North Korea if it continues to flout international demands to halt its nuclear program.

Pyongyang demonstrated once again this week it has no intention to heed those threats. In a press statement issued shortly after North Korea set off its third nuclear test on Monday, Pyongyang responded to the chorus of international condemnation with the usual bluster: North Korea, the statement asserted, has been forced to develop a nuclear deterrent to counter what it calls a "hostile" U.S. campaign to threaten its existence, and deprive it of what it sees as its legitimate right to launch satellites into space.

"If the United States makes the situation complicated by remaining hostile through the end we will have no choice but to take serial measures with more intense second and third response," the statement warned. It added that the interdiction of North Korean vessels "will be instantly regarded as an act of war and will lead to our relentless retaliatory strikes on their bases."

Susan Rice, the U.S. ambassador to the United Nations, hit back, pledging a "swift, credible, and strong response by way of a Security Council resolution that further impedes the growth of DPRK's nuclear weapons and ballistic missile programs and its abilities to engage in proliferation actions."

But Rice encountered immediate resistance from China during the council's closed door session on Tuesday. China's deputy U.N. envoy, Wang Min, said that Beijing was firmly opposed to North Korea's action and underscored the importance of a nuclear-free Korean peninsula. But he also sought to water down the council's response, initially arguing that the nuclear test posed no threat to international peace and security and needed to be addressed through dialogue with the government.

Wang ultimately yielded on that point after Rice read out North Korea's statement to the council, in which she posed a simple question: How can North Korea's nuclear test, coupled with a threat to strike out at the United States, not constitute a threat to international peace and security?

But Wang secured a concession -- the removal of a provision underlining the council's intent to begin negotiation of a Security Council resolution under Chapter Seven -- that signaled China's ongoing reluctance to impose further sanctions on North Korea. (Chapter Seven is the provision in the U.N. Charter that it invokes for the imposition of sanctions). In its place, the council issued a statement pledging to consider "appropriate measures" in response to Pyongyang's action. Western diplomats noted that previous North Korean nuclear tests have resulted in Chapter Seven resolutions, and it would be unthinkable that a resolution adopted in response to the latest test would not be under Chapter Seven.

So what measures could the U.N. Security Council take, short of military action (which virtually no country advocates), to convince North Korea to halt its nuclear program?

North Korea is already perhaps the most isolated country in the world. Its trade is scrutinized at foreign ports. Ships carrying North Korean supplies are routinely boarded and searched. Its banks largely shy away from doing business in the world's main financial markets.

Rice provided few details, saying simply that the United States would seek to "tighten" and "augment" a set of existing sanctions aimed at limiting North Korea's capacity to develop its weapons programs. The U.S. envoy recalled that the Security Council had just warned Pyongyang last month that it would face "significant action" from the council if it launched a ballistic missile or tested a nuclear weapon. "And indeed, we will do so," she assured reporters.

Turtle Bay has compiled a list of possible sanctions targets:

• For a start, the U.N. Security Council could strengthen a set of financial sanctions that are designed to restrict North Korea's access to international financial markets. In January, the council adopted a resolution that calls on governments to "exercise enhanced vigilance" in preventing their nationals from engaging in financial transactions linked to North Korea's ballistic missile or nuclear program. Those provisions could be made mandatory.
• The Security Council sanctions are primarily targeted at North Korean ballistic missile and nuclear technology. Sanctions could be expanded to hit other segments of North Korea's already ailing economy. While this approach could increase economic pressure on the leadership in Pyongyang, it would likely contribute to even further hardship and suffering for ordinary North Koreans, with limited chance of changing government behavior. The North Korean leadership has been willing to allow its people to endure extreme hardship, and China would never assent to a sanctions strategy that threatened to tip North Korea into chaos, triggering a potential exodus of starving citizens across the border into China.
• Expand the category of goods that North Korea cannot trade. The U.N. Security Council has identified a long laundry list of dual-use industrial items -- from vacuum pumps to high grade maraging steel -- that can potentially be used in a ballistic missile program or in the construction of centrifuges. David Albright, president of the Institute for Science and International Security, said that the council could tighten the chokehold by expanding the prohibition on the range of prohibited items. "I think it works better to simply say all goods that could be used in a nuclear program are prohibited," Albright said. "It's easier to detect and enforce. And it will cause a lot more disruption in their supply chain."
• When the Security Council wants to ratchet up pressure on North Korea it has periodically added the names of individuals and companies to its sanctions black list. The North Koreans have sought to circumvent that move by creating front companies and changing the names of enterprises hit with financial sanctions. Expect to see the council add to that list.
• The U.N. Security Council has already imposed fairly comprehensive arms embargo on North Korea. But there is one glaring exemption: small arms. China has blocked previous efforts to include these weapons. Look for that exemption to come up for review.
• Infuriated by North Korea's 2006 nuclear and ballistic missile tests, Japan then quietly floated a proposal for a naval blockade on North Korea. The initiative never saw the light of day and is almost certainly not going to get past this time around. "It's a bridge too far," said one diplomat, explaining that virtually no one thinks it's sensible to cut off the already isolated government entirely, saying it could fuel mass starvation.
• The U.N. Security Council has already provided states with wide scope to search vessels transporting North Korean goods at port. The search and seizure provision has served to harass North Korean shippers, leading to the seizure of prohibited goods. The U.N. has not authorized states to board vessels in international waters -- a step that would bring the council into conflict with the seafaring protections contained in the Law of the Sea. And there is little chance that the council will push any further in that direction.

The 800-pound gorilla in the debate about the effectiveness of any sanctions is China. By the end of 2010, the last date for which there are records, China's trade with North Korea had boomed, surpassing $3.06 billion, up nearly 10 percent over 2008, according to figures cited by a U.N. panel monitoring enforcement of the North Korea sanctions.

A major share of North Korea's imports arrive via the Chinese port of Dalian, or across the border by land. George Lopez, a professor of peace studies at Notre Dame University and former member of a Security Council panel monitoring North Korea sanctions, said China could have a major impact on the sanctions if it enforced them more aggressively.

For instance, he said, they could conduct random inspections of goods entering the country, and they apply pressure on Chinese companies that trade with the north not to supply prohibited goods. Chinese banks, he added, could choose to clamp down on financial transactions by firms suspected of violating sanctions. But he said the United States may have to convince Beijing that it recognizes its interest in forestalling a collapse of the North Korean economy, and provide greater assurances that it has no intention to back the downfall of the regime in Pyongyang.

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