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18. The Proliferation Security Initiative: international law aspects of the Statement of Interdiction Principles



I. Introduction

II. Development of the Proliferation Security Initiative

III. The Statement of Interdiction Principles

IV. Conclusions

Appendix 18A. The PSI Statement of Interdiction Principles


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In the aftermath of the terrorist attacks against the USA on 11 September 2001, and the subsequent focus on proliferation of weapons of mass destruction (WMD) to state as well as non-state actors, there has been a growing consensus on the need to take more robust measures against proliferators. One such measure is the interception of goods and technologies in transit. In particular, the USA has stressed that effective interception is a critical part of its strategy to combat weapons of mass destruction and their delivery systems.


However, the So San incident in 2002 demonstrated that international law places important limits on interception activities. The incident gave an important impetus for US authorities to formulate a policy response that would pave the way for more robust action against proliferators in future. In May 2003 US President George W. Bush announced a new multilateral initiative focusing on law enforcement cooperation for the interception and seizure of illegal weapon and missile technologies. This initiative became known as the Proliferation Security Initiative (PSI). Thus far, only a limited number of states participate in the ‘core group’ of this initiative, while a significant number of states have expressed support for the principles that have been developed within its framework.


The PSI developed quite rapidly in 2003 and 2004. The PSI’s main output thus far is the Statement of Interdiction Principles, which establishes important limitations on states’ authority to exercise enforcement jurisdiction against vessels suspected of carrying WMD and related items. The majority of the commitments contained in the statement comply with existing international law. Nevertheless, the development of the PSI has brought to the fore the challenge of reconciling two interests that, at least prima facie, appear difficult to reconcile. Taking robust and creative steps to prevent the proliferation of WMD would imply changes to and new developments of the existing rules and principles of international law. However, most governments seem to prefer to take these measures within existing domestic and international legal frameworks, which might not support overly robust and creative steps. The process of developing the PSI seems to have resulted in a change in emphasis within the initiative—from a recognition of the need to change the law to a focus on what actions might legally be taken under existing international and domestic legislation.


The PSI participating states have tried to acquire legal authority by means of UN Security Council resolutions or amendments to conventions that do not directly deal with the fundamental rules and principles of the law of the sea. In order to gain legitimacy, however, the process needs to be more inclusive with regard to participation. Furthermore, the process should directly focus on the most relevant treaty—the UN Convention on the Law of the Sea.