U.S. President Donald Trump’s intensifying economic campaign against Iran is testing the limits of the security grouping Chinese President Xi Jinping and Russian President Vladimir Putin have spent years expanding as a counterweight to U.S. power.

The Chinese and Russian presidents will gather with their Iranian counterpart, Masoud Pezeshkian, for the first time since the start of the U.S. and Israeli war against the Islamic Republic at the Shanghai Cooperation Organization summit that starts Monday in Kyrgyzstan. Indian Prime Minister Narendra Modi will also attend along with leaders from Central Asian states, Pakistan and Belarus.

“The message is getting clearer and louder each year that there’s emerging a new security bloc,” said Henry Wang Huiyao, founder of the Center for China and Globalization research group in Beijing. The unipolar world dominated by the U.S. “is gone,” he said.