After Mr. Pompeo’s announcement, Foreign Minister Mohammad Javad Zarif of Iran said on Twitter that the United States was an “outlaw regime.” He praised the court’s ruling earlier, saying it marked “another failure” for the “sanctions-addicted” United States and “victory for rule of law.”

In legal terms, the United States withdrawal from the 1955 treaty with Iran does not take effect immediately. The treaty remains in place for one year from any announcement of withdrawal, meaning Iran’s lawsuit will proceed.

It was negotiated after the C.I.A. helped stage a coup in Iran that Iranians still cite as a gross violation of the country’s sovereignty. The 1953 coup, code-named Operation Ajax, was engineered by Kermit Roosevelt Jr., a grandson of President Theodore Roosevelt, and installed a government that two years later cemented the treaty with President Dwight D. Eisenhower.

The treaty sets up commercial relationships, tax structures and access to each nation’s courts. None of that has applied since the 1979 Islamic revolution.

“The treaty with Iran is a weird treaty,” said Julian Ku, a professor of constitutional and international law at Hofstra University Law School. “We haven’t been friends with Iran in a long time.”

Mr. Ku said there have been two other instances since the 1980s in which the United States withdrew from a treaty after an unfavorable ruling by the International Court of Justice. One was during the Reagan administration, in a case brought in 1984 by Nicaragua; the second was in 2005, when the George W. Bush administration lost a case brought by Mexico.



Lawyers for the United States had argued that the sanctions dispute with Iran was a matter of American national security, and therefore the court had no jurisdiction to intervene. Rulings by the International Court of Justice are legally binding but difficult to enforce; in the past, both the United States and Iran have ignored its orders.