The U.S. launched what it described as an unprecedented campaign to cripple Iran's economy by cutting off "every remaining lifeline" sustaining the country.

Yet unmentioned in Scott Bessent's speech announcing "Operation Economic Outcast" was the country that has enabled Iran to withstand years of American pressure: China.

The announcement Monday by the U.S. Treasury secretary-which included penalties against companies enabling Iran but fell short of more forceful sanctions on China-illustrates the challenge for Washington in squeezing Tehran economically.

Iran relies on China to buy most of its oil. Beijing has, in turn, established an elaborate system to move the sale proceeds around the world without triggering U.S. sanctions. But Washington so far has proven reluctant to seriously confront Beijing over its support for the U.S. enemy.

"The rhetoric was ferocious, but the punch less so," said Daniel Fried, a former U.S. diplomat now at the Atlantic Council. "Dealing a crippling blow to Iran's economy would probably require taking on big Chinese firms and banks."

As part of its new effort to end the war with Iran, the U.S. sanctioned more than 60 entities, including Chinese firms that enable Iran to procure nuclear and missile technology, earn revenue from oil and carry out cyber operations.

The latest U.S. initiative builds on more than 1,000 sanctions the Trump administration has placed on Iran since returning to power last year. The effort, alongside military operations and a naval blockade of Iranian ports, has damaged Iran's economy, collapsing its currency.

But the U.S. so far has failed to change Tehran's aggressive military posture in the Middle East or deter it from seeking nuclear weapons.

Bessent said President Trump is making phone calls to world leaders to request they stop doing business with Iran and warned the U.S. would also soon sanction an unnamed financial institution for sanctions evasion. Sanctions generally aim to cut off targets from the U.S. financial system, turning them into economic pariahs and threatening companies that dare to trade with them.

The Treasury also said Monday it would levy future penalties on countries and entities that do business with Iran in five sectors: digital assets, technology, gold, aviation and shipping.

"Treasury structured the whole thing to give China room to adjust quietly," said Kerri Bitsoff, a former Treasury official. The "framing means China can change behavior without its banks being targeted," she said.

Since the war against Iran began, the U.S. has sanctioned Chinese oil tankers and oil infrastructure, though China has continued to purchase Iranian oil.

Although the U.S. blockade has limited Iranian oil exports recently, China imported more than 500,000 barrels a day so far in August, according to Kpler. Much of this originates from an elaborate system involving ship-to-ship transfers of Iranian oil, which often move Iranian oil from sanctioned tankers onto unsanctioned ones. Those tankers then ship the oil to China.

Whether Chinese banks and refineries judge Bessent's threats credible will be critical. Trump has made improved relations between the U.S. and China a priority following a major tariff war last year. China at the time responded with powerful tools of its own, including restricting access to rare earths, which pummeled U.S. manufacturers.

China has repeatedly said it opposes "illegal and unreasonable unilateral sanctions" by Washington. A foreign ministry spokesman reiterated that message in a press briefing Tuesday, saying economic warfare will only heighten tensions and could disrupt the global economy.

China "will take all necessary measures to firmly safeguard its rights and interests," the spokesman, Lin Jian, said.

Chinese retaliation "is a real threat now," said Edward Fishman, a senior fellow at the Council on Foreign Relations in New York City. "That's a whole new factor in the U.S.-China dynamic as of last year."

Trump visited Xi Jinping in May in Beijing and the Chinese leader is expected in Washington next month for a follow-up summit.

Even as the White House has sought better relations with Beijing, the U.S. has called out China's role in undercutting efforts to isolate Iran.

China and Iran have established a complex system aimed at evading U.S. sanctions. U.S. officials have said China buys more than 80% of Iranian oil exports and warned that Iranian front companies use Chinese banks to buy Chinese goods and move cash via currency exchange houses to the Middle East and Iran.

The effort to isolate Iran economically from the U.S. dollar has also forced the regime to increasingly use China's currency, the yuan, to trade, blunting the effect of U.S. sanctions.

The U.S. effort has increasingly resembled a game of whack-a-mole. The Treasury has sanctioned little-known firms and shell companies in Hong Kong, China, the United Arab Emirates and Turkey, only for other players to emerge as facilitators of Iranian oil sales, money flows and imports from China to the Middle East.

On Monday the U.S. sanctioned a China-owned oil tanker it says has transported millions of barrels of Iranian oil to China this year, as well as China and Hong Kong-based companies and individuals that helped Iran obtain sensitive goods, like navigation instruments for missiles. But the U.S. didn't target any prominent Chinese banks or companies that are more clearly connected and reliant on the U.S.-led global financial system.

During the press conference announcing sanctions, Bessent was asked twice whether the administration would strengthen sanctions against Chinese banks and businesses.

"Every country, every entity should know that they should be prepared to face U.S. sanctions," Bessent said. "No one is above this."

Bessent has said that the administration's new pressure campaign seeks to create the conditions for regime collapse in Iran. Bessent dubbed the initiative Economic D-Day, likening the effort to the World War II campaign.

"Nothing close to the hype," said Charlie Brown, a researcher with United Against Nuclear Iran, a U.S. advocacy organization that is calling for more sanctions against banks in China and elsewhere that facilitate the purchase of Iranian oil.

It is possible the campaign could cajole China into doing more to pressure Iran, while avoiding a more direct confrontation between the world's biggest economies.

"This sort of pressure can work, and I have seen it be more effective than actual sanctions," said Bitsoff, the former Treasury official. "The test will likely be after the summit."