The US Treasury Department announced in a statement it was sanctioning a "teapot refinery" based in China's Shandong province that bought Iranian oil worth "approximately half a billion dollars."

Teapot refineries are small, privately owned operations in China and stand in contrast to the larger state-owned enterprises in the country.

Beijing hit back on Friday, accusing the United States of "undermining the normal trade and economic cooperation between China and Iran."

US President Donald Trump has reinstated a campaign of "maximum pressure" against Iran since returning to office and has already rolled out sanctions against several individuals and entities, including the country's oil minister.

The oil in question was transported by Iran's "shadow fleet" of tankers, according to the Treasury Department, including from ships linked to the Huthis and to the Iranian ministry of defense of armed forces logistics, MODAFL.

The Treasury Department also sanctioned an additional 19 ships and companies responsible for supplying the refineries.

"Teapot refinery purchases of Iranian oil provide the primary economic lifeline for the Iranian regime, the world's leading state sponsor of terror," Treasury Secretary Scott Bessent said.

The US State Department unveiled its own sanctions against a Chinese oil terminal on Thursday.

"These sanctions are being imposed pursuant to President Trump's maximum pressure campaign to drive Iran's oil exports, including to China, to zero," State Department spokesperson Tammy Bruce said in a statement.

"China is by far the largest importer of Iranian oil," she said, adding that Tehran used these oil revenues to "finance attacks" against US allies and to support terrorism around the world.

Asked about the moves on Friday, China's foreign ministry said Beijing "has always opposed the abuse of illegal unilateral sanctions and long-arm jurisdiction."

"China will take all necessary measures to resolutely safeguard the legitimate rights and interests of Chinese enterprises," ministry spokeswoman Mao Ning said at a regular news briefing.