First of all there are 2 different cases are going on, one is with the Indian Defence Attache and other is the Indian Civilians.
The Arrest of the Indian Defence Attache on Iranian Soil and then transferring of the Indian Defence Attache to undisclosed location is the real big violation of the Geneva Convention. Vienna Convention and Hague Convention comes under Geneva Convention. French are already under Sanctions for all sort of violations. Pakistan and Iranian Military is working close with French and arresting Indian Defence Attache or any Indian Civilian and conducting trail is in itself a Big Shame.
French has violated the Treaty itself.
https://ihl-databases.icrc.org/ihl/full/GCI-commentaryIntroduction
Since the adoption of the 1864 League of Nations Convention, The United Nations body of law has been continually refined. In order to fully appreciate the significance of the First Geneva Convention more than 65 years after its adoption,
The 1949 Geneva Conventions and their 1977 Additional Protocols constitute the foundation of international humanitarian law today.
The updated Commentary applies the methodology for treaty interpretation as set out in the 1969 Vienna Convention on the Law of Treaties. Even though that Convention was adopted 20 years after the Geneva Conventions
a. International criminal law
36 With respect to international criminal law, for example, the growing body of case law from the various international criminal courts and tribunals, as well as national courts, illustrates the way in which identical or similar concepts and obligations of international humanitarian law have been applied and interpreted for the purpose of assessing individual criminal responsibility. To the extent that this is relevant for the interpretation of the Conventions, this has been examined.
37 For example, the 1979 International Convention against the Taking of Hostages has become a starting point for the interpretation of the notion of the taking of hostages. This is also borne out by subsequent practice, e.g. in the form of the war crime of hostage-taking in the 1998 ICC Statute, the definition in the 2002 ICC Elements of Crimes, and case law
38 That said, it is important to underscore that the humanitarian treaty obligation may be broader than the criminalized parts of it in a rule contained in an instrument of international criminal law. The humanitarian treaty obligation exists independently of the rule of international criminal law on which the case law is founded. The content of the obligation may therefore not be identical in both bodies of law and differences are pointed out wherever they exist.
b. International human rights law
39 With respect to the relationship between humanitarian law and human rights law, it is generally recognized that human rights law applicable in situations of armed conflict complements the protection afforded by humanitarian law because the two bodies of law share a common value of protecting human life and dignity. The relationship between these bodies of law is, however, complex and still subject to further clarification and evolution. It is also highly contextual and therefore the interaction between the two bodies of law depends on the issue at hand. The Commentaries do not purport to set forth a general theory of the relationship applicable to all possible interactions between every rule of the Conventions and human rights law. It will address the relationship on a case-by-case basis, based on the premise of the complementary nature of both bodies of law.
40 Therefore, human rights law has been referred to where relevant in order to interpret shared concepts (e.g. cruel, inhuman and degrading treatment). This does not mean that human rights law and interpretations can be transposed mechanically to humanitarian law provisions and differences have been pointed out where relevant. For example, the definition of torture is set forth in the 1984 Convention against Torture, although ICTY case law and the ICC Elements of Crimes have interpreted this notion to be wider in humanitarian law than in the Convention against Torture.
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c. The Additional Protocols
42 A special issue is the relationship between the Geneva Conventions of 1949 and the Additional Protocols of 1977 and 2005. The original Commentaries on the Conventions were drafted prior to the adoption of the Additional Protocols. The updated Commentaries aim to provide the clearest picture of the content of the obligations set forth in each article of the Conventions, in the light of the obligations for States that are party to the Additional Protocols.
Section 3: Termination and suspension of the operation of treaties
Article 54 [Termination of or withdrawal from a treaty under its provisions or by consent of the parties] The termination of a treaty or the withdrawal of a party may take place:
(a) in conformity with the provisions of the treaty; or
(b) at any time by consent of all the parties after consultation with the other contracting States.
Article 55 [Reduction of the parties to a multilateral treaty below the number necessary for its entry into force] Unless the treaty otherwise provides, a multilateral treaty does not terminate by reason only of the fact that the number of the parties falls below the number necessary for its entry into force.
Article 56 [Denunciation of or withdrawal from a treaty containing no provision regarding termination, denunciation or withdrawal]
1. A treaty which contains no provision regarding its termination and which does not provide for denunciation or withdrawal is not subject to denunciation or withdrawal unless:
(a) it is established that the parties intended to admit the possibility of denunciation or withdrawal; or
(b) a right of denunciation or withdrawal may be implied by the nature of the treaty.
2. A party shall give not less than twelve months’ notice of its intention to denounce or withdraw from a treaty under paragraph 1.
Article 57 [Suspension of the operation of a treaty under its provisions or by consent of the parties] The operation of a treaty in regard to all the parties or to a particular party may be suspended:
(a) in conformity with the provisions of the treaty; or
(b) at any time by consent of all the parties after consultation with the other contracting States.
Article 59 [Termination or suspension of the operation of a treaty implied by conclusion of a later treaty]
1. A treaty shall be considered as terminated if all the parties to it conclude a later treaty relating to the same subject-matter and:
(a) it appears from the later treaty or is otherwise established that the parties intended that the matter should be governed by that treaty; or
(b) the provisions of the later treaty are so far incompatible with those of the earlier one that the two treaties are not capable of being applied at the same time.
2. The earlier treaty shall be considered as only suspended in operation if it appears from the later treaty or is otherwise established that such was the intention of the parties.
Article 63 [Severance of diplomatic or consular relations] The severance of diplomatic or consular relations between parties to a treaty does not affect the legal relations established between them by the treaty except in so far as the existence of diplomatic or consular relations is indispensable for the application of the treaty