By Aresu Eqbali in Tehran and Sune Engel Rasmussen in Beirut 

Iran's supreme leader said his country wouldn't back down in the face of U.S. sanctions, days after President Trump targeted him personally with a new round of measures to further isolate the country.

Ayatollah Ali Khamenei on Wednesday called U.S. pressure "obvious tyranny" and labeled Washington the "most hated, evil government in the world," demonstrating how the U.S. and Iran remain locked in a standoff over Tehran's nuclear program and American economic sanctions.

"The Iranian people are not surprised by these ugly actions of the U.S. and do not back down," he said.

Mr. Khamenei didn't address the sanctions against him. The U.S. has said it took action against the Iranian leader and his office and associates for their alleged role in destabilizing the Middle East through such actions as promoting terrorism and targeting U.S. vessels. Washington also issued sanctions against eight senior officials from Iran's Islamic Revolutionary Guard Corps and said it would add to the sanctions list the country's top diplomat, Foreign Minister Javad Zarif, later this week.

"The U.S. move to put the name of the supreme leader of the revolution and the people associated with his office in the sanctions list shows this reality that they are completely unfamiliar with international regulations," Mr. Zarif was quoted by Iran's IRNA news agency as saying on Wednesday.

The sanctions are unlikely to significantly affect Mr. Khamenei who doesn't travel internationally and, according to Erich Ferrari, founder of Ferrari & Associates PC, a law firm representing Iranian and other targets of U.S. sanctions, doesn't have any known assets abroad. The head of Iran's central bank, Abdolnaser Hemmati, on Wednesday said the sanctions wouldn't affect Mr. Khamenei.

However, Mr. Khamenei is believed to control a vast financial empire inside Iran, known as Setad. Iranian officials depict Setad as a charity, while the U.S. Treasury calls it a "massive network of front companies" hiding assets for the Iranian leadership. The U.S. previously issued sanctions against Setad in 2013.

Mr. Ferrari said the sanctions on the supreme leader would tighten economic pressure on Iran by adding to the already-considerable risk facing foreign companies still doing business there.

Sanctions against Mr. Zarif probably would have a broader political impact. The foreign minister, whose diplomacy was key in reaching the landmark 2015 nuclear deal, regularly travels to the U.S. to speak at think-tank events and maintain diplomatic contacts, which would likely be impossible if he is blacklisted, Mr. Ferrari said.

But the U.S. will likely be obligated by its international agreements to allow Mr. Zarif to attend United Nations events.

The sanctions against Iran's head of state were the latest volley in a growing American campaign to coerce Iran to negotiate for a broad agreement superseding the 2015 deal to limit its nuclear program, from which Mr. Trump unilaterally withdrew last year. The U.S. has since imposed a series of economic sanctions aimed mostly at Iran's banks and its large oil industry, and also built up its military presence in the Persian Gulf in response to what Washington officials said were Iranian threats.

Acrimony between Washington and Tehran continues to grow. Most notably, the U.S. has accused Iran of sabotaging six tankers in the Gulf of Oman in two separate attacks, which Iran denies. Iran last week downed an American surveillance drone, which Iran says was in its airspace but which the U.S. says was over international water.

Iran has said the sanctions against Mr. Khamenei ruled out any prospect of diplomacy. The supreme leader and other officials have rejected an offer from Mr. Trump to negotiate, saying the U.S. can't be trusted. At the same time, Mr. Trump has threatened Iran with an overwhelming military response if it takes any further action against American targets.

As economic pressure has battered the Iranian economy, slashing its oil exports by some 80% since this time last year, Tehran has said it would disregard limits on stockpiles of uranium and heavy water set in the 2015 nuclear deal. The move is an attempt to pressure the European parties to the deal, including France, the U.K. and Germany, to deliver some of the economic benefits Tehran expects.

Iranian state television quoted the spokesman for Iran's atomic agency, Behrouz Kamalvandi, as saying the country would speed up the enrichment of uranium beginning on Thursday, ignoring the 300-kilogram (660-pound) limit on stockpiles set in the 2015 deal.

He also said Iran could start enriching uranium beyond the purity limit of 3.67% set by the same deal on July 7. Uranium with a purity level of 90% is considered weapons-grade, which Iran has always maintained it didn't seek.

"There is still time for the Europeans. But if they want more time, it means either they can't or don't want to comply with their commitments," Mr. Kamalvandi said.

Write to Sune Engel Rasmussen at sune.rasmussen@wsj.com

(END) Dow Jones Newswires

June 26, 2019 15:14 ET (19:14 GMT)

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