Editor's Note: (Ernest J. Moniz was the US secretary of energy from 2013 to 2017. Sam Nunn was a US senator from Georgia from 1972 to 1997. They are co-chairmen of the Nuclear Threat Initiative. The opinions expressed in this commentary are their own.)

(CNN) The United States and North Korea are increasingly at risk of military conflict -- most probably through an accident or miscalculation, but possibly a deliberate decision.

Opportunities for diplomacy are narrowing. Leaders from the United States, South Korea and Japan have recently stated now is not the time for dialogue with Pyongyang -- even though any strategy other than war for halting and reversing North Korea's nuclear and missile programs must, at some point, include talks.

So, when is the time for dialogue with North Korea to avoid a war no one wants and end a nuclear program that endangers the world? How does the Trump administration's threat to pull out of the agreement with Iran to end its nuclear program impact North Korea diplomacy?

Sam Nunn

Ernest J. Moniz

Today's growing dangers require a policy response that minimizes the risk of a catastrophic conflict, both directly from North Korea's nuclear and missile program and from our attempts to halt its progress.

It is imperative that we focus now on steps to reduce these risks, including first and foremost the risk of use of nuclear weapons, but also of devastating conventional forces on both sides of the 38th parallel. Unlike with Iran, where it made sense to keep the talks confined to the nuclear program in order to prevent nuclear weapons development, North Korea negotiations must address broader issues.

Henry Kissinger argued recently that diplomacy must begin with a common understanding between Washington and Beijing on goals and strategy for negotiations with North Korea. Work on this common understanding should be our focus. The beginning goal: China's full implementation of the sanctions it has already agreed to and the United States entering a parallel track of talks with Pyongyang, which President Trump should make clear he is ready to do as a key element of a coordinated approach.

For the talks with North Korea to succeed, the United States and China must first share a vision of the ultimate goal -- and the political, economic and security arrangements needed at various stages along the way. That shared vision with Beijing must be built on a strong framework of consultation between the United States, South Korea and Japan, and other key parties, including Russia.

We must be prepared to engage Beijing on issues it has raised and its fears: These include the potential for the collapse of the government in North Korea leading to a massive refugee crisis, US and allied missile defense, large-scale military exercises and US long-term military posture on and around the Korean Peninsula. In this context, reunification of the Korean Peninsula is not an obtainable goal for the foreseeable future.

To bolster the diplomatic track, all parties involved must strictly enforce all United Nations Security Council resolutions targeting the North's illicit activities. This is fundamental to maximizing our leverage with Pyongyang for meaningful negotiations. It is vital to China's credibility, and the credibility of the United Nations Security Council. And it is crucial to restricting resources and materials that can aid North Korea's nuclear and missile programs, as well as preventing the export of dangerous nuclear materials by North Korea. With this foundation in place, diplomacy with Pyongyang can proceed.

To reduce the risk of blundering into a war that could badly damage South Korea and devastate North Korea, US leadership is essential. The Trump administration should agree to enter informal initial discussions with North Korea, without preconditions.

Washington should also make it clear that our ultimate goal of a nuclear-weapons free Korean Peninsula, agreed to and verified by the international community, remains constant -- and use these talks to explore how we can reduce interim risks and move forward with six-party negotiations.

While DPRK nuclear weapons and delivery systems must be a primary focus of six-party diplomacy, addressing conventional military threats, including addressing the artillery tubes trained on Seoul, is also core to any successful negotiation. The near-term goal therefore should be an agreement that halts advances in North Korea's nuclear weapons and missile programs and provides the foundation for a more comprehensive rollback.

Such an agreement could include the basic parameters of a nuclear and missile freeze to halt any further significant development of the North's nuclear and missile capabilities, including provisions for robust monitoring and verification. Achieving a verifiable freeze will of course require calibrated movement on political, economic or security issues of interest to North Korea. Ultimately, the goal is to establish a step-by-step process that addresses the security needs of all parties.

The United States' credibility for diplomacy with China, our allies and our adversaries will be crippled if the United States unilaterally pulls out of the Iran agreement without clear and compelling evidence of Iranian noncompliance. Why would North Korea engage in new talks, or reach any new agreement, with the Trump administration? Even before then, why would our negotiating partners, in particular China and Russia, line up shoulder to shoulder with the US government to pressure North Korea, when the United States walks away from its commitments?

North Korea has gotten this far with its nuclear and missile programs in part because of the unique geopolitical circumstances of the Korean Peninsula, where there remains the very real danger of a conventional war with millions of casualties on both sides of the 38th parallel. North Korea, South Korea, or the United States -- knowingly or unknowingly -- could cross an ill-defined tripwire with horrific consequences. Fully enforcing sanctions while actively pursuing diplomacy with China, our allies and Russia -- and then with Pyongyang -- is urgent and essential for global security. Only the United States can realistically catalyze a success-oriented strategy for all parties.