The presiding judge of the U.N. body informally known as the World Court began the hearing by calling on Washington to respect its outcome. During their decades of animosity, both the United States and Iran have ignored some rulings at the court.

The lawsuit filed with the ICJ says the U.S. sanctions, which are damaging the already weak Iranian economy, violate terms of a little-known friendship treaty between the two countries.

“The U.S. is publicly propagating a policy intended to damage as severely as possible Iran’s economy and Iranian national companies, and therefore inevitably Iranian nationals,” said Mohsen Mohebi, representing Iran, at the start of four days of oral hearings. “This policy is plainly in violation of the 1955 Treaty of Amity.”

He said Iran had sought a diplomatic solution to the countries’ dispute but was rejected.

The United States said in an initial written reaction displayed in court that it believes the ICJ has no jurisdiction in the case, and that Iran’s assertions fall outside the bounds of the treaty.

U.S. lawyers led by State Department adviser Jennifer Newstead, appointed by Trump in 2017, are due to respond on Tuesday. A ruling is expected within a month, though no date has been set.

The ICJ is the United Nations tribunal for resolving international disputes. Its rulings are binding, but it has no power to enforce them.

U.S. President Donald Trump pulled out of a 2015 pact between Iran and major world powers under which sanctions were lifted in return for Tehran accepting curbs on its nuclear program. The Trump administration then announced unilateral plans to restore sanctions against Tehran.

Although Washington’s European allies protested against Trump’s move, most Western companies intend to adhere to the sanctions, preferring to lose business in Iran than be punished by the United States or barred from doing business there.

The United States and Iran have clashed at the court in the past since they became enemies after Iran’s 1979 Islamic Revolution. Iran ignored a 1980 U.S. suit at the ICJ over the seizure of American diplomats in Tehran, which the court found to be illegal.

In another suit and countersuit, the ICJ found that the 1955 treaty was still valid even though it was signed before the revolution. However, the court found in 2003 that neither actions by the United States against Iranian oil platforms nor Iranian attacks on American shipping violated the treaty.

At the start of Monday’s hearing, the court’s president, Abdulqawi Yusuf, leading a 15-judge panel, urged the United States to adhere to any provisional decision the court may make.

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