Secretary of State Mike Pompeo made a rare appearance at the United Nations Security Council on Wednesday, putting aside his publicly stated skepticism of the organization as he sought to broaden support for the hard-line American stance on Iran.

In particular, he accused Iran of having destabilized the Middle East and beyond, through what he described as the “reckless” development of ballistic missiles systems.

Iran, he said, had embarked on a “proliferation spree” and now possessed the largest ballistic missile arsenal in the Middle East, with weapons capable of carrying several warheads and striking American military bases in the region, as well as some European capitals.

He faulted the Iran nuclear deal, the Obama-era accord that President Trump withdrew from in May, for giving Iran access to funding streams that Mr. Pompeo said had been directed to its military.