BEIJING — China has rejected the Trump administration’s latest sanctions targeting Iran’s aviation sector, calling unilateral U.S. sanctions “illegal” and signaling that Beijing will not accept Washington’s efforts to extend its restrictions to companies and countries doing business with Tehran.
Chinese Foreign Ministry spokesman Guo Jiakun said Tuesday that China “consistently opposes illegal unilateral sanctions that lack a basis in international law or authorization from the UN Security Council.” 
His remarks came after U.S. Treasury Secretary Scott Bessent
 threatened to cut foreign companies and airports off from the U.S. financial system if they provide fuel, landing services or ticket sales to Iranian airlines.
The Chinese response reflects a broader disagreement over how Iran should be treated economically—and highlights the increasingly important role Beijing plays in keeping Tehran connected to international markets.
The dispute comes as China remains Iran’s most important economic partner. A recent analysis by Foreign Policy described China as central to Iran’s ability to withstand Washington’s sanctions campaign, particularly because of Beijing’s continued purchases of Iranian oil and the financial and commercial networks linking the two countries.
According to Foreign Policy, China accounts for roughly 90 percent of Iran’s oil exports. Much of that trade is carried through a shadow fleet of vessels and other mechanisms designed to reduce exposure to Western sanctions. China’s role as Iran’s principal oil customer gives Tehran an important source of revenue even as Washington attempts to restrict its access to international markets.
Beijing also provides an alternative financial environment. Iran can make use of commercial and financial channels connected to China, including the Cross-Border Interbank Payment System, or CIPS. While CIPS is not a complete replacement for the global dollar-based financial system, its existence provides Iran with another channel through which international transactions can be conducted with less dependence on Western financial institutions.
That relationship helps explain why Beijing’s latest rejection of the U.S. aviation measures carries significance beyond the airline industry.
The United States can impose sanctions on Iranian companies, but China’s willingness to continue trading with Iran makes economic isolation unlikely. Foreign Policy has said that substantially greater pressure on Tehran would eventually require Washington to confront major Chinese banks, refineries, shipping companies and other businesses involved in Iranian commerce.
Such pressure would put Beijing in a position where defending its economic relationship with Iran could increasingly become part of its broader dispute with Washington.
China, however, has significant reasons to maintain its relationship with Tehran. Iran is an important source of relatively discounted oil for Chinese buyers, while Chinese companies have developed extensive commercial links with the Iranian economy. At the same time, Beijing has economic leverage of its own because Iran depends heavily on China as a market for its oil.
The relationship does not mean China controls Iran’s economic or foreign policy. But it does give Beijing an important position within the network of external economic relationships that allows Tehran to continue trading despite U.S. sanctions.
The aviation dispute therefore represents another test of China’s willingness to resist Washington’s pressure. Bessent’s warning seeks to make companies around the world choose between continuing to serve Iranian airlines and maintaining access to the U.S. financial system. Beijing’s response indicates that China does not intend to accept the U.S. position as an internationally binding obligation.
The timing also adds a diplomatic dimension. Bessent met Chinese Vice Premier He Lifeng in New York on Sept. 20 for economic and trade discussions, shortly before the latest Chinese criticism of the Iran sanctions. President Donald Trump and Chinese President Xi Jinping are also expected to meet later this week.
For Beijing, the Iran issue is therefore intertwined with a broader question of economic sovereignty: whether Washington should be able to determine which Chinese companies, banks and trading partners can participate in commerce with countries under U.S. sanctions.