Article 43 Vienna Convention on the Law of Treaties

Obligations imposed by international law independently of a treaty

The invalidity, termination or denunciation of a treaty, the withdrawal of a party from it, or the suspension of its operation, as a result of the application of the present Convention or of the provisions of the treaty, shall not in any way impair the duty of any State to fulfil any obligation embodied in the treaty to which it would be subject under international law independently of the treaty.

See also: Article 42 Vienna Convention on the Law of Treaties