The United States rolled out a blitz of sanctions on Friday, targeting 40 shipping firms and vessels that it identified as being part of Iran’s so-called shadow fleet of oil tankers, as the Trump administration broadened its efforts to cripple the Iranian economy.

The Trump administration also imposed sanctions on an independent Chinese refinery, Hengli Petrochemical Refinery, which is one of Iran’s largest customers for crude oil and other petroleum products.

“Treasury will continue to constrict the network of vessels, intermediaries and buyers Iran relies on to move its oil to global markets,” Treasury Secretary Scott Bessent said in a statement released by the department. “Any person or vessel facilitating these flows — through covert trade and finance — risks exposure to U.S. sanctions.”

The United States has dramatically changed its approach to sanctions on Iran in recent weeks. After granting a monthlong exemption to sanctions that allowedi the sale of some Iranian oil in March, the Trump administration imposed more aggressive sanctions, in addition to mounting its own blockade of the Strait of Hormuz in parallel to Iran’s. The reversal was intended to choke off the oil revenue that Iran uses to power its economy.

Iran relies heavily on its shadow fleet of tankers to evade Western sanctions in transporting oil to Asia.

Much of the Iranian oil that is sold to China is purchased by its independent “teapot” refineries. Hengli is China’s second largest such refinery, and it has purchased billions of dollars’ worth of Iranian crude from the Revolutionary Guards Corp, which wields pervasive military, political and economic clout throughout Iran.