In a talk at the Harvard Belfer Center on 6 April, I argued that it is time to get serious about North Korea, by giving concerted, high-level attention to both sanctions and diplomacy. Pyongyang’s failed test launch of the medium-range mobile ballistic missile dubbed the Musudan underscores the danger and the need.

Over the past three years, world leaders focused intently on the Iranian nuclear challenge, and through a careful combination of incentives and disincentives succeeded in bottling up any Iranian nuclear-weapons option for the next 15-plus years. North Korea presents a far more serious nuclear challenge.

Unlike Iran, North Korea makes no bones about having an active nuclear-weapons programme. It has clearly violated the Nuclear Non-Proliferation Treaty (NPT) as well as international norms against nuclear testing. It also clearly seeks an intercontinental ballistic missile (ICBM).

Separating the reality of North Korea’s strategic programmes from the regime’s bluster is not easy. The outlandishness of the hermit kingdom’s boasts makes it tempting to pooh-pooh their capabilities.

We do not know much about their hardware, and we know less about the internal dynamics of the system. Whether the nuclear devices are entirely based on plutonium, and how far their uranium enrichment programme has progressed, remains unknown. The absence to date of test launches of their longer-range missile systems and of re-entry tests underscores the guesswork nature of assessments. Such uncertainty works to the regime’s benefit, because its deterrence and political purposes are served to the extent that adversaries believe they have powerful weapons.

But just because Pyongyang wants us to pay attention, that doesn’t mean we shouldn’t. While an ICBM threat to the US homeland is still years away, North Korea today presents a clear and present danger to its immediate neighbours. Its Nodong missiles are a proven system which can hit all of South Korea and much of Japan. Armed with a crude 1,000kg warhead, the Nodong  can fly 900km – not quite to Tokyo, but the range covers Japan’s capital if the warhead mass can be reduced to 750kg, a task Pyongyang has probably mastered. The Nodong variant displayed in October 2010 could probably fly 1600km, meaning it could also hit US bases on Okinawa, which is likely to be North Korea’s strategic objective.

Concerned states need to take effective action to halt further progress in the North’s strategic weapons programme. Such action has already begun. South Korean President Park Geun-hye’s difficult decision in February to close the Kaesong industrial zone after North Korea’s fourth nuclear test showed how seriously Seoul is taking the issue. China’s agreement to impose tough UN sanctions on 2 March and then to implement them showed a new seriousness as well. But UN Security Council Resolution 2270 has loopholes that now need to be closed, including by banning all coal exports, not just those that funnel money into the strategic programmes.

As important as it is that China stops underwriting the Kim regime through its trade and investments, it is wrong to presume that China alone holds the key to stopping the North's threatening behaviour. At a recent workshop in Washington DC on North Korea it was claimed, bizarrely to my mind, that the role of third parties – meaning China – is vital, yet the US could itself do little to change the regime's nuclear trajectory. China believes the opposite. In fact, both views are exaggerated.

Sanctions alone will not be sufficient. Negotiations over Iran's nuclear programme succeeded because of a combination of sanctions and incentives. Both sides made compromises. US Secretary of the Treasury Jacob Lew recently warned against ‘sanctions overreach’ - relying too much on sanctions without a broader strategy for achieving foreign-policy goals. He was referring to the Iran case, but the same applies to North Korea.

Concerned states must not rush to offer a deal immediately after the nuclear and missile tests. To do so would encourage Pyongyang to continue such provocations. At some point, however, high-level engagement is needed. It may be too late for the Obama administration to put in place an engagement strategy with North Korea. But it would be very helpful to his successor if he began the effort.

Washington has certainly tried to engage before, with temporary success. In 1994, bilateral talks produced the Agreed Framework; in 2005, Six Party Talks produced a joint statement in which North Korea agreed to denuclearisation, and the US and Japan agreed to begin work toward normalisation. In 2012, bilateral talks produced the Leap Day deal in which the North agreed to a moratorium on nuclear tests, enrichment activity and missile launches. The circumstances in which North Korea eventually broke each deal provided lessons on Pyongyang’s duplicity but also showed how each deal could have been improved.

Unlike the Iran case, the major powers may not have a partner in Pyongyang willing and able to accept compromises. Kim Jong-un, whose schooling in Switzerland gave reason to hope he would bring reforms, now seems more akin to Stalin than to Gorbachev. But we don’t know. It is preposterous that only the American to get to know him is Dennis Rodman .

High-level engagement need not mean major concessions that imperil national interests. North Korea should not be accorded recognised status as nuclear-armed. But its adversaries can engage in peace-treaty talks, as long as South Korea is involved, and there is no presumption of any change to the US–South Korea alliance. A peace regime does not necessarily mean departure of US forces.

North Korea probably will not trade away its nukes, but it may agree again to freeze the programme. It should also agree on no transfer of weapons technology. Internal verification is problematic, but interdiction efforts of the type used in the Proliferation Security Initiative can enforce the existing ban.

The United States has to be careful not to signal that it only cares about containment, and not denuclearisation, which must remain the goal. If diplomacy does not work, concerted effort to put pressure on North Korea will be ramped up. Efforts to sharpen the regime’s choices serve a longer-term goal of hastening internal conditions in North Korea for changing the nature of its government, ideally through unification with the South.

Mark Fitzpatrick is Executive Director of IISS-Americas.