(AP) — Ambassadors from the United States and China exchanged barbs at the World Trade Organization on Thursday over the countries’ simmering trade dispute.

The showdown between Dennis Shea and Zhang Xiangchen came at a WTO meeting in Geneva on Thursday, as the two massive economies are embroiled in a trade war. The Trump administration is putting tariffs on billions worth of Chinese goods, and China is retaliating.

Shea lashed out at Beijing’s claim that it supports open, transparent, inclusive and non-discriminatory trade. He said: “China’s size magnifies the harm caused by its state-led, mercantilist approach to trade and investment, and this harm is growing every day and can no longer be tolerated.”

Zhang replied that Shea had “made the air smell like gunpowder.”

“We should thank Ambassador Shea, as he reminded us that we are now in an unprecedented crisis of the multilateral trading system,” he said.

While noting issues of poverty in China, Shea rejected Chinese government claims that it remains a developing country given that it is the world’s largest automotive market, oil importer, steel manufacturer and meat consumer. He insisted that the Chinese state retains control or strong influence over a wide array of businesses in China.

“We want to ensure that members truly understand that change is necessary if the WTO is to remain relevant to the international trading system,” he said, insisting that China too must change to “fully and effectively embrace open, market-oriented policies like other WTO members.”

The meeting was closed to reporters and the comments were made available to The Associated Press through their respective diplomatic missions.

Trump has repeatedly criticized the WTO as allegedly unfair to the U.S.

Zhang then all but accused the U.S. of being the bigger disrupter of trade with its tariffs on steel, aluminum and tens of billions of dollars’ worth of Chinese goods.

“We have to be fully aware which country’s trade measures are most disruptive,” he said.