After previously not supporting the resolution by France, Germany, and the United Kingdom against Iran over its nuclear program, the United States has since changed course and now supports the resolution, as part of a broader strategy.
US Ambassador to International Organizations in Vienna Laura Holgate explained this was due to three developments.
First, "Iran has thus far failed to provide the legally required cooperation necessary to resolve long outstanding safeguards issues involving evidence of nuclear material at undeclared locations."
Second, "there is a deeply troubling and steady drumbeat of recent statements from senior Iranian officials threatening that Iran may reconsider its stated nuclear doctrine and asserting that Iran has all the technical capabilities needed to quickly to build nuclear weapons should it decide to do so."
Third, "Iran has repeatedly responded to the resolutions adopted by this Board in recent years with escalation instead of cooperation, including by producing 60 percent enriched uranium at its heavily fortified, underground facility at Fordow."