US President Donald Trump on Sunday threatened China with “staggering” 50% tariffs if it provides military assistance to Iran, raising the specter of further friction between the world’s two largest economies.

Beijing has cast itself as a peacemaker and reportedly helped broker the temporary US-Iran ceasefire, but has also been playing a more active role in the conflict in recent weeks, The New York Times reported: US intelligence suggests China may have shipped missiles to Iran, a report Beijing strongly denied.

While energy supply disruptions raise costs for China’s manufacturers, some in Beijing think the war is damaging American strength, drawing Washington’s attention away from Asia.

The issue threatens to complicate Trump’s planned visit to China next month.