International law admits the use of force against terrorist groups which are hardly referable to a specific State only under certain circumstances. This could happen when a State is unable to repress terrorist organisations operating in its territory and, furthermore, when it clearly asks the international community for some intervention in order to fight these groups. However the use of force should be proportionate and necessary to deter the specific threat at hand.

In addition, State practice shows that, in face of organisations on the terrorist nature of which there is a consensus at the international community level, it is not necessary to demonstrate a strict link between them and a particular State. To the contrary it seems that one or more States can use force against another State when the latter gives shelter to terrorist organisations in its territory and does not provide adequate measures in order to repress them, despite the repeated requests to do so by the international community.

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