to prevent transfers of concern; and in May 2005 Ulrik Federspiel, Denmark’s ambassador to the United States, asserted that "the shipment of missiles has fallen significantly in the lifetime of PSI." However, references such as these provide no actual information on or evidence of interdictions which have occurred, leaving critics to remain skeptical of such numbers or of any "metrics" that prove the effectiveness of the initiative. While these criticisms persist, many PSI events, such as annual Operational Experts Group meetings, contain a very high degree of civil society participation. Think tanks and industry representatives, for instance, participated in the 2016 Operational Experts Group meeting and were permitted to Tweet throughout. Responses to criticism Much of the criticism about the PSI have been faced with counter-arguments, given the inaccurate or outdated nature of much of the information about the initiative. The most common negative portrayal of PSI represents it as an illegal, US-led effort to interdict third party vessels on the high seas. PSI proponents have countered that: United Nations Security Council Resolution (UNSCR) 1540 places an international obligation on all Members of the UN to take action against the proliferation of WMD, and its language matches closely with the PSI Statement of Interdiction Principles. UNSCRs 1874 (on the DPRK's WMD program) and 1929 (on Iran's WMD program) explicitly call on or require UN Members to take interdiction and inspection actions against WMD-related materials that are consistent with PSI's principles. Thus inspection of such vessels are international mandates rather than "piracy," as accused by DPRK and Iran. Article 4 of the 2005 Protocol to the Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation illegalize the illicit transfer of WMD-related materials by maritime vessel. The 2010 International Civil Aviation Organization (ICAO) "Convention on the Suppression of Unlawful Acts Relating to International Civil Aviation" and "Protocol Supplementary to the Convention for the Suppression of Unlawful Seizure of Aircraft" illegalize the illicit transfer of WMD-related materials by aircraft. Contrary to comments that the PSI works "outside" of international frameworks such as the United Nations, UN officials including Secretary General Kofi Annan have "applaud[ed] the efforts of the Proliferation Security Initiative to fill a gap in our defenses." In February 2004, the PSI was "expanded" beyond a military and intelligence effort to include greater cooperation with law enforcement entities. PSI has largely evolved from a focus on interdiction of