Days after brokering a rapprochement between Iran and Saudi Arabia, Xi Jinping struck a triumphant note. China should “actively participate” in “global governance” and “add more stability and positive energy to world peace”, he told Beijing’s rubber-stamp legislature on Monday.

Xi’s achievement was in convincing Tehran and Riyadh to restart diplomatic relations after almost seven years, a shift that caught many across the Middle East and in Washington by surprise.

But just as significant may be what the diplomatic breakthrough revealed about Washington’s limits as the region’s dominant power, and China’s potential willingness to assume a more political role, mediating peace deals and shaping the security architecture as the US once did.

Chinese experts see the Iran-Saudi detente as a potential turning point. If the deal — which includes resuming bilateral economic and security agreements — is implemented smoothly, the region “will have even higher expectations towards China, and China’s confidence that it can face these expectations will increase,” said Fan Hongda, a professor at the Middle East Studies Institute of Shanghai International Studies University.

Such ambition would represent a marked shift. Beijing has acted as a primarily economic partner in the Middle East. Its energy procurements have ballooned from 3 per cent of the region’s oil exports to 30 per cent over the past 30 years, and it is the biggest buyer of Saudi and Iranian crude oil.

That has given China considerable clout as a trading partner — Saudi Arabia’s largest — and source of investment. China is also one of the world’s few major powers to have healthy relations with Iran, with which the US has not had formal diplomatic ties since 1980.

Xi attended summits with Arab leaders in Riyadh in December, and he hosted Iranian president Ebrahim Raisi in Beijing last month.

“Middle Eastern countries are increasingly hoping that China can go beyond economic engagement and should help solve security problems,” Fan said.

But to many in the west, Beijing’s growing diplomatic ambition will be seen foremost as a challenge to US supremacy in the Middle East.

The deal comes at a time of testy relations between Saudi Arabia and Joe Biden’s administration, with some Gulf states noting that their traditional partner has been disengaging from the region.

Saudi Crown Prince Mohammed bin Salman has been pursuing an assertive foreign policy as he seeks to balance the kingdom’s ties to Washington with its growing relationships with China and other Asian powers.

One US diplomat in Asia said Beijing was trying to exploit the shift in Washington’s foreign and security policy from a decades-long focus on the Middle East to the Indo-Pacific.

“They are clearly pushing into the gap they think our retreat is leaving,” the diplomat said, echoing Biden’s pledge in Riyadh last July that “we will not walk away and leave a vacuum to be filled by China, Russia, or Iran”.

China has presented itself as a benign alternative to a US hegemon. In 2016, Xi told Arab League officials that China would “not use proxies” or “engage in creating spheres of influence”. Instead, it invited countries to “join the Belt and Road Initiative’s circle of friends”, which it cast as “a network of mutually beneficial partnerships”.

Other analysts see a big gap between lofty rhetoric and sustainable peace deals. Jesse Marks, a non-resident fellow on China-Middle East relations at the Stimson Center think-tank and a former adviser in the Office of the Secretary of Defense, questioned the agreement’s longevity.

“Saudi-Iran competition has been going on more or less since the 1979 revolution in Iran, and there may be no more than short-term tactical considerations for them to agree to a deal now,” he said. He added that Riyadh and Tehran’s backing of rival factions in Yemen and Lebanon could put strains on the deal.

Over the past six years, Beijing has repeatedly floated vague Middle East peace proposals addressing the Israeli-Palestinian conflict, the Syria crisis and a new security architecture for the entire region.

In a recent position paper on the war in Ukraine, Beijing similarly restated calls for dialogue, disappointing those who hoped that it might take up a more active role as a peacemaker. The question of China’s engagement is set to resurface if, as reports suggest, Xi visits Russia next week.

Foreign policy experts argue that China has too few diplomats to transform its sweeping statements into substantive diplomacy. “People assume that China is like the US with all the oil and trade relations, but we have not seen them exert the leverage,” Marks said.

A European diplomat said that Beijing could try to emulate Russia in the Middle East as “a spoiler for western initiatives”, adding: “But it can be attractive to some governments in the region and in some cases they can do what the US can’t — like in the case of sitting down with Iran to do a deal with Saudi.”

For Beijing, the advantages of broadening ties its in the region beyond energy are numerous. On his trip to Saudi Arabia in December, Xi proposed agreements ranging from health to defence dialogue. China’s only overseas military base is in Djibouti, just across a narrow strait from the Arab peninsula.

“The fact that the US has influence, or even control, over certain countries in the Middle East poses a risk to China,” said a Chinese security analyst who asked not to be named because they are not cleared to speak to foreign media. The analyst added that if Beijing imposed a trade quarantine or blockade on Taiwan, Washington might retaliate by pressing its Middle Eastern allies to suspend oil shipments to China or acquiesce to a US blockade.

Other Chinese experts believe such concerns could even shape Beijing’s policy.

Niu Xinchun, director of the Institute of Middle East Studies at the Chinese Institutes of Contemporary International Relations, said in an online discussion last week that although Beijing was reluctant to compete with the US in the Middle East, where it believed Washington enjoyed a decisive advantage, the toxic bilateral relationship might force it to do so. He said: “China’s Middle East policy is actually at a crossroads.”