“The United States has a set of sanctions that preclude crude oil from being shipped to any country,” Mr. Pompeo told reporters at the Security Council. “We’ve made clear, anyone who touches it, anyone who supports it, anyone who allows a ship to dock is at risk of receiving sanctions from the United States.”

Iran’s United Nations ambassador, Majid Takht Ravanchi, who also spoke at the Security Council meeting, attributed the Middle East’s instability to what he described as the history of American interventionism and Washington’s support for Israel and Saudi Arabia.

The United States, he said, had “persistently sowed division between the regional countries,” and “the Iranophobic statements of the U.S. officials serve also the same purpose.”

The tensions between the United States and Iran have raised fears of a new armed conflict in the Middle East.

All other major powers, including the American allies Britain and France, support the 2015 nuclear agreement with Iran and have urged the United States to rejoin it. The agreement limited Iran’s nuclear activities in return for an end to most economic sanctions against the country.

The Trump administration has argued that the agreement is weak and merely delays the time when Iran would be able to make a nuclear weapon. The administration’s position is not widely shared. Iran promised under the agreement that it would never seek nuclear arms.

Mr. Trump’s declarations of success in some other high-profile issues — notably in terminating the Islamic State and ending the menace of North Korea’s nuclear and missile capabilities — have faced increased skepticism.