A state can only extend diplomatic protection to its own nationals. There must be no doubt as to the nationality of the injured party. In addition, nationality must be continuous. The person concerned must be a national at the time of the injury and at the time the complaint is lodged.
Multiple nationality can be an obstacle to diplomatic protection. In principle, diplomatic protection may not be exercised against another state of which the injured party is also a national, as the person concerned is regarded by that state as its own national. Furthermore, the Swiss authorities can only protect the rights of Swiss citizens with dual nationality vis-à-vis third states if their Swiss nationality is predominant. The International Court of Justice pronounced on the establishment of predominant nationality in the Nottebohm case.
The Nottebohm case
An intervention by Switzerland with the state of nationality is however conceivable in the case of serious and repeated violations of fundamental principles of international law as defined in the European Convention on Human Rights or according to international customary law (i.e. the right to life, the right to physical integrity and the prohibition of torture, the right to a fair trial).
A state has two criteria for determining the nationality of a legal person with the purpose of extending diplomatic protection: the registered office of the company and the predominant control of the company.
Breach of international law
For diplomatic protection to be exercised, the injury suffered must be the result of a breach of international law by the host state. Examples include the denial of justice, imprisonment without trial, discriminatory or arbitrary expropriation, nationalisation or confiscation without compensation.
The prior exhaustion of remedies
A state can only provide diplomatic protection and seek a remedy or file a complaint if the person concerned has already exhausted all local remedies to the extent possible and as could be reasonably expected. The effect of this condition is to turn diplomatic protection into a subsidiary mechanism. It would be premature for one state to accuse another state of a breach of international law if it had had no opportunity to right the wrong.
The prior exhaustion of remedies in the responding state is not required in all circumstances, for example where there are no available, effective or adequate local remedies.
Diplomatic protection cannot be extended if the prescription period has expired. The same applies if the claim of the home state of the injured person has failed.