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More than two years have elapsed since North Korea and the United States have had a meaningful diplomatic exchange on Pyongyang’s nuclear and missile programs. Any attempt by the United States or others to resume negotiations with North Korea on its nuclear and missile programs would be predicated on understandings about what activities are compatible with in-depth talks. Part of these understandings would be a freeze on certain missile-related activities, both to create the political space for constructive, in-depth talks and to prevent Pyongyang from further enhancing its missile arsenal in the meantime.

Options for a Freeze

The scope and extent of a freeze would depend on what sort of agreement can be reached, and verification requirements would follow from that agreement. Three broad options exist: freezing the testing of rocket engines or missiles; freezing the production of new missiles, launchers, or platforms; and freezing the deployment of new missiles, launchers, or platforms. In addition to providing greater or lesser benefits, these options can be assessed in terms of the United States’ ability to verify them, their acceptability to North Korean officials, and the negotiating parties’ ability to put them in place on short notice.

Joshua H. Pollack
Joshua H. Pollack is the editor of the Nonproliferation Review and a senior research associate at the James Martin Center for Nonproliferation Studies of the Middlebury Institute of International Studies at Monterey. He is a leading expert on nuclear and missile proliferation, focusing on Northeast Asia.

A Test Freeze

Testing rocket engines—with either ground tests or flight tests—is crucial for developing and evaluating new types of missiles and establishing their reliability. However, a significant drawback is that freezing these types of tests would do little to keep North Korea from expanding its missile force using proven designs.

Verification of a flight-test freeze for ballistic missiles is straightforward. Infrared detectors already in geosynchronous orbit above the Eastern Hemisphere can reliably verify the absence of these tests (or space launches, which are functionally similar). These highly capable systems are expressly designed to spot the heat plumes of rocket boosters as they lift ballistic missiles out of the earth’s atmosphere. However, it is not well understood how reliably they can detect ground tests of these engines, which could take place under cloud cover or even inside enclosed structures. It is also not well understood how reliably infrared satellites can detect the flight testing of ground-launched or sea-launched cruise missiles, which use small rocket boosters to get into the air. These missiles could be flight-tested below cloud cover.

Such verification issues have arisen in past negotiations with Pyongyang. Possibly with the question of cloud cover in mind, North Korea voluntarily facilitated U.S. verification of a testing freeze in 2018 by removing the upper parts of its largest ground-testing stand for liquid-propellant rocket engines. The partly disassembled structure could be monitored by imagery satellites, providing further assurance that no ground tests were being conducted there.

A Production Freeze

The expansion or modernization of North Korea’s missile forces could be held in check through a freeze on manufacturing activity, assuming sufficient knowledge of the locations of the production facilities involved.

Because the absence of sustained activity at specific sites can be observed with imagery satellites, the closure of entire industrial facilities could be readily verified with existing capabilities. It would not be nearly as simple to verify the partial closure of a facility or selective restrictions on the products leaving an active facility. To help verify compliance with the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, the United States and the Soviet Union developed what was termed a continuous portal monitoring system that involved a standing U.S. presence at the gates of the main Soviet rocket engine plant, but this system took considerable time to negotiate and implement.

A Deployment Freeze

The expansion or modernization of North Korean missile forces could also be held in check by a freeze on deployments of new or additional systems to missile operating bases.

Unfortunately, the absence of new deployments would be difficult to verify reliably in the absence of onsite inspections at missile operating bases, which North Korea would be unlikely to accept. North Korea has never declared the numbers or locations of these bases, although open-source researchers have identified at least some of them in commercial space imagery. These sites are found in remote mountain valleys, are heavily camouflaged, and are largely underground. Imagery satellites could be used to watch for new construction at previously identified bases, but they obviously cannot characterize what sort of equipment is kept inside a tunnel or under a roof. A similar observation applies to submarines, which can be stored inside coastal tunnels when they are not at sea.

Trade-offs and Constraints

There are at least three major constraints on the scope and duration of a freeze and its associated verification measures. These include what the United States (and other negotiation partners) might be willing to offer in exchange for a freeze, how intrusive the associated verification measures would be, and how protracted the negotiation and implementation of those verification measures would be.

First, how much North Korea would be prepared to give up depends on what it can get. If the United States (or any other negotiating partner) wishes to ask for more, it would probably have to offer more. These sorts of trade-offs are not always announced explicitly, but they can nevertheless be observed in the diplomatic record. For example, the de facto freeze on missile testing that North and South Korea agreed to for the duration of the Olympic Games in early 2018 appears to have been implicitly conditioned on the nearly simultaneous announcement that no U.S.–South Korean combined military exercises would be held that spring.

Second, apart from the scope and duration of the freeze itself, more intrusive verification measures would be harder to get. Onsite inspections at military facilities would be difficult to negotiate under the best of circumstances, a limitation that tends to rule out any verified freeze on deployments.

Third, more complex verification arrangements, even if they are acceptable to North Korean officials, would take time to negotiate and implement. Measures that involve an onsite presence for foreign inspectors or the installation of monitoring equipment at production facilities might be useful as part of a subsequent agreement. Because a freeze is meant to create suitable conditions for a protracted diplomatic process, it should involve only those measures that can be implemented promptly.

Consequently, the forms of verification most suitable for an initial freeze are limited to the use of U.S. national technical means (such as satellites), potentially supplemented by voluntary measures undertaken in North Korea. This category could include a freeze on flight tests and space launches, ground tests of engines, or all activities at selected production facilities.


Based on what the United States believes it would need to enable serious negotiations, and what it is prepared to offer North Korea in exchange, a range of options may be identified.

Perhaps the single most essential step, a freeze on ballistic missile flight tests and space launches, could readily be verified from space. This freeze could apply to all missiles above a certain minimal range, or it could be limited to long-range missiles and space launches only. Long-range missiles would include the large inter-continental ballistic missile displayed in North Korea’s October 2020 military parade, a missile that appears to be intended to serve as North Korea’s first “multi-warhead rocket.”

Focusing on long-range missiles and space launches would address the single most pressing military concern for the United States, and such an approach might require fewer concessions than an across-the-board testing freeze. Conveniently, such a testing freeze would also be consistent with the precedent of Kim’s April 2018 announcement of a unilateral and voluntary suspension of all nuclear tests and long-range missile tests. (Although Kim has said that this suspension is no longer in effect, he has continued to abide by it.) On the other hand, such a narrow freeze would not address the most pressing military concerns of Japan and South Korea, who could argue that it represents a step away from the repeated demands of the United Nations Security Council for North Korea to abandon all ballistic missiles. Such a narrow arrangement might also fall short of satisfying the core political goal of a freeze: reducing tensions to create room for comprehensive negotiations.

Beyond seeking a freeze on the flight testing of all types of missiles (to be verified with national technical means alone), the United States could also seek a freeze on ground tests. Satisfactory verification of the absence of ground tests would be more likely to require North Korea to undertake voluntary measures.

The same observation might apply to a freeze on production at key facilities, if Pyongyang is willing to halt all work at given sites for an agreed-upon duration. This option appears to be the most extreme that might realistically be considered for a freeze arrangement. Because of the intrusiveness or complexity of the associated verification measures, neither a freeze on new deployments at military facilities nor selective restrictions on activities at production facilities appear feasible.

Note: This piece draws upon analysis in the following co-authored paper. See Joshua H. Pollack, Miles Pomper, Ferenc Dalnoki-Veress, Joy Nasr, and Dave Schmerler, “Options for a Verifiable Freeze on North Korea’s Missile Programs,” James Martin Center for Nonproliferation Studies, CNS Occasional Paper #46, April 30, 2019,