Accusing Washington of "strangling" its economy, Tehran has asked the court in The Hague to order Washington to lift the measures, reimposed after US President Donald Trump pulled out of a multilateral 2015 accord.

Despite its long enmity with the United States, Iran brought the case under a 1955 "friendship treaty" that predates the country's Islamic Revolution.

Washington has forcefully told the court, which rules on disputes between United Nations member states, that it has no jurisdiction to rule on the case as it concerns a matter of national security.

The ruling on Wednesday at 0800 GMT -- in the grand surroundings of the 1913-built Peace Palace in the Dutch city -- follows four days of hearings at the end of August.

Rulings by the ICJ are binding and cannot be appealed, but it has no way to enforce its decisions.

"If the court orders measures, they should be respected," Eric De Brabandere, a professor of international law at the University of Leiden, told AFP.

If the court decides it has jurisdiction, it will likely "declare that the parties should refrain from aggravating the dispute", but any steps beyond this remain to be seen, he said.

The 2015 nuclear deal saw Iran agree to limit its nuclear programme and let in international inspectors in return for an end to years of sanctions by the West.

But Trump pulled out of the deal in May, to the dismay of European allies, arguing that funds from the lifting of sanctions under the pact had been used to support terrorism and build nuclear-capable missiles.

- 'Economic warfare' -

At the United Nations General Assembly last week, Trump denounced the deal as "horrible" and "one-sided".

During the ICJ hearings, Iran said the sanctions reintroduced in September are causing economic suffering for its citizens. US lawyers retorted that economic mismanagement was at the root of Iran's woes.

A second wave of US measures is due to hit Iran in early November, targeting its vital oil exports.

Experts said the Iran-US case was an important opportunity for the ICJ to rule on the issue of "economic warfare" -- not currently designated as a use of force.

The case "may offer the court sufficient legal basis to indicate a limit under international law to coercion by the US," Geoff Gordon, an international law expert at the Asser Institute in The Hague, told AFP.

"International law, for reasons to do with power politics, has never formally recognised economic warfare to be a use of force as prohibited by the UN Charter, though economic sanctions can have the same effects and worse as guns and bombs."

But he warned that "the decision is likely to be occasion for escalating tensions."

Relations have plunged to a new low since Trump's election, even as the US president reaches out to North Korean leader Kim Jong-un over his nuclear programme.

Trump and Iranian President Hassan Rouhani faced off at the UN last week, with Rouhani denouncing leaders with "xenophobic tendencies resembling a Nazi disposition."

Despite their 1955 Treaty of Amity and Economic Relations, Iran and the United States have not had diplomatic ties since 1980.

The ICJ was set up in 1946, after the carnage of World War II, to rule in disputes between countries.