The United States accused Tehran Monday of having "unclean hands" as it fought an Iranian court bid to unfreeze billions of dollars earmarked by Washington for terror victims, AFP reported.
Washington said Iran's "support for international terrorism", including bombings and airline hijackings, should rule out its case at the International Court of Justice (ICJ) in The Hague.
Iran dragged Washington to the UN's top court in 2016 over a US Supreme Court ruling that the $2 billion should go to victims of attacks blamed on Iran.
Iran said the case breached a 1955 "Treaty of Amity" between Washington and Tehran signed before Iran's revolution.
Washington tore up that treaty last week after the ICJ in a separate case ordered the United States to ease sanctions reimposed on Iran by US President Donald Trump after he pulled out of Iran's 2015 international nuclear deal.
"Iran comes to the court with unclean hands. Indeed, it is a remarkable show of bad faith," Richard Visek, a US State Department legal official, told the court.
"The actions at the root of this case centre on Iran's support for international terrorism... Iran's bad acts include supports for terrorist bombings, assassinations, kidnappings, and airline hijackings," he said.
Visek also accused Iran's "most senior leaders" of the "encouragement and promotion of terrorism" and "violation of nuclear non-proliferation, ballistic missile and arms trafficking obligations".
Iran's use of the 1955 treaty to lodge the case was an "abuse of process", he added.