On January 18, 2019, IOSCO (International Organization of Securities Commissions), which is a quasi global standard setter for the world's capital markets (it counts among its members the US SEC and its equivalents from around the world), issued a statement on disclosure of ESG matters.  Although not a statement about integrated reporting per se, it does suggest that issuers voluntarily disclose material ESG disclosures.  They reference a number of frameworks and standards that issuers can follow as a guide for these material disclosures, including the IIRC, as well as TCFD, GRI and CDP, among others.

You can read the online statement on IOSCO's web site here: https://www.iosco.org/library/pubdocs/pdf/IOSCOPD619.pdf