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Applying Necessity and Proportionality to Anti-Terrorist Self-Defence

  • Christian J Tams (a1) and James G Devaney (a2)

Recent years have seen increasing reliance on self-defence as a concept justifying the use of force against armed attacks by terrorists operating from within a foreign state. While the matter has prompted major debates, a good case can be made that contemporary international law now begins to recognise a right of self-defence against attacks by terrorists. (We will refer to this in the following as ‘anti-terrorist self-defence’, meaning a response directed against an attack carried out by a terrorist organisation.) This article deliberately does not rehearse the major debates about the scope of self-defence, but moves beyond them. It seeks to assess whether and how the two main limitations on the exercise of self-defence – namely necessity and proportionality – could be adapted to self-defence outside the inter-state setting. It shows that both limitations do indeed require some adaptation in order to be applied to anti-terrorist self-defence.

With respect to necessity, we argue that this adaptation is actually a chance to make sense of a requirement that is of very limited practical relevance in the inter-state setting. As the article shows, necessity can assume a crucial role in the anti-terrorist setting: in order for trans-border uses of force to be necessary, states invoking self-defence must demonstrate that the terrorist threat cannot be repelled by the host state (on whose territory the terrorists are based).

As for proportionality, recent debates about anti-terrorist self-defence expose the weaknesses of proportionality as a restraint on self-defence. Construed primarily as a prohibition against excessive force, even in the inter-state setting, proportionality has always been dependent on the nature of the aims pursued in the name of self-defence. Recent anti-terrorist practice suggests that many states are prepared to accept far-reaching uses of force against terrorists. It also suggests that, in applying proportionality, the targeted (or otherwise) character of the response is of crucial importance. The law is clearly in a state of flux, but in debates such as those about Turkey's use of force against the PKK or Israel's military operations against Hamas or Hezbollah, one can see the beginning of a process of developing guidelines on proportionality.

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Noam Lubell , Extraterritorial Use of Force against Non-State Actors (OUP2010) 64

Antonio Cassese , ‘Terrorism is also Disrupting Some Crucial Legal Categories of International Law’ (2001) 12 European Journal of International Law 993

Sean D Murphy , ‘Self-Defense and the Israeli Wall Opinion – An Ipse Dixit from the Court?’ (2005) 99 American Journal of International Law 62

Tom Ruys and Sten Verhoeven , ‘Attacks by Private Actors and the Right of Self-Defence’ (2005) 10 Journal of Conflict and Security Law 289

Constantine Antonopoulos , ‘Force by Armed Groups as Armed Attack and the Broadening of Self-Defence’ (2008) 55 Netherlands International Law Review 159

Christian J Tams , ‘Light Treatment of a Complex Problem’ (2005) 16 European Journal of International Law 963

Kimberley N Trapp , ‘The Use of Force against Terrorists: A Reply to Christian J. Tams’ (2009) 20 European Journal of International Law 1049

Christian J Tams , ‘The Use of Force against Terrorists: A Rejoinder to Federico Sperotto and Kimberley N. Trapp’, (2009) 20 European Journal of International Law 1057

Ruth Lapidoth , ‘The Legal Effect of Security Council Resolution 1701 (2006) on Cessation of Hostilities in Lebanon’ in Andreas Fischer-Lescano and others (eds), Frieden in Freiheit = Peace in liberty = Paix en liberté: Festschrift für Michael Bothe zum 70. Geburtstag (Nomos/Dike2008)

Thomas Franck , ‘On Proportionality of Countermeasures in International Law’ (2008) 102 American Journal of International Law 715

TD Gill , ‘The Temporal Dimension of Self-Defence: Anticipation, Pre-Emption, Prevention and Immediacy’ (2006) 11 Journal of Conflict and Security Law 361

Abdul Ghafur Hamid , ‘The Legality of Anticipatory Self-Defence in the 21st Century World Order’ (2007) 54 Netherlands International Law Review 441

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Israel Law Review
  • ISSN: 0021-2237
  • EISSN: 2047-9336
  • URL: /core/journals/israel-law-review
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