A/HRC/42/CRP.1 Group received no evidence as to the existence of a mechanism that was effectively investigating allegations of violations. 900. The Group is not aware of any alleged perpetrator having been held accountable by parties to the conflict for a crime related to the conflict, despite a request for information to this effect addressed to the Government of Yemen, members of the coalition, and the de facto authorities. In a few cases, the Group of Experts has gathered evidence that the Government of Yemen has attempted to hold alleged perpetrators accountable by starting investigations, including in setting up special committees for this purpose. However, such investigations have been undermined by the lack of capacity and the fear of reprisals. Accordingly, it appears that none of the parties to the conflict is either willing or able to carry out investigations or prosecutions, in violation of their obligations under international law, especially in view of alleged war crimes. 901. In the absence of any international jurisdiction being seized of the situation in Yemen, the Group of Experts recommends that the Human Rights Council renew and strengthen its mandate with regard to the collection and preservation of evidence. 3. Responsibility of third States 902. According to Article 1 Common to the Four Geneva Conventions, State parties have the duty not only to respect the Conventions, but also to ensure their respect, in all circumstances. This provision has been interpreted as providing that “States, whether neutral, allied or enemy, must do everything reasonably in their power to ensure respect for the Conventions by others that are Party to a conflict”.1434 The obligation to respect and ensure respect is not limited to the Geneva Conventions, but extends to the entire body of international humanitarian law. In particular, it is now recognized as customary law that States may not encourage violations of international humanitarian law by parties to an armed conflict, and that they must exert their influence, to the degree possible, to stop such violations.1435 903. It is further generally acknowledged that the duty to ensure respect for the Four Geneva Conventions, and for international humanitarian law in general, encompasses both negative and positive obligations.1436 Regarding negative obligations, State parties are expected to abstain from certain conduct, i.e. they must not encourage, aid or assist in violations of the Conventions. As for positive obligations, parties must take reasonable measures to prompt States that violate the Conventions to act in compliance with international humanitarian law.1437 904. The fact that international humanitarian law obligations can be considered erga omnes means that all States have a legal interest in their observance. This represents another basis for the obligation to respect and ensure respect of international humanitarian law, as expressed in Common Article 1 of the Geneva Conventions. 905. At the very least, this may require States to raise concerns. The duty to raise concerns over compliance, without it being perceived as an unfriendly act, may be derived from the erga omnes character of IHL obligations. 1438 If IHL obligations are not simply of a bilateral nature but represent undertakings owed to the international community as a whole, members of that community must have the standing to express concern regarding non1434 ICRC commentary to article 1 common to the Geneva Conventions, 2016, para. 153. See ICRC Study on Customary IHL, rule 144. 1436 See ICRC Study on Customary IHL, rule 144 (commentary); See ICRC, International Humanitarian Law and the Challenges of Contemporary Armed Conflicts, Geneva, December 2003, p. 47 (www.icrc.org/eng/assets/files/other/ihlcontemp_armedconflicts_ final_ang.pdf); Knut Doermann and Jose Serralvo, “Common Article 1 to the Geneva Conventions and the obligation to prevent international humanitarian law violations”, International Review of the Red Cross (2014), 96 (895/896), 707–736 (https://www.icrc.org/en/international-review/article/common-article-1) 1437 See ICRC commentary to article 1 common to the Geneva Conventions, 2016, para. 154. 1438 Erga omnes obligations are owed towards the international community as a whole and are not merely bilateral obligations, as is the case with much international law. IHL is not reciprocal in character. 1435 216