US President Donald Trump's decision to block ship traffic through the Strait of Hormuz presents China with a sticky choice: to accept Trump's prohibition on trade with Iran, Beijing's staunch ally, or challenge the closure and turn this Middle East conflict into a duel between nuclear-armed superpowers.

China had largely watched the joint US-Israeli war on Iran, now more than six weeks old, from the sidelines. It had criticized the massive bombing campaign, observed Trump's difficulty in bending Iran to his will, while enjoying cut-rate Iranian supplies of crude oil and natural gas that freely traversed the strait into the Indian Ocean.

That scenario faces a new and dangerous moment. To maintain its fossil fuel supply and also show Iran that their alliance is worth preserving, China must challenge the American blockade. Trump says the strait will remain closed until all ships, including those of America's Arab allies, can pass through freely.

Zineb Riboua, a Middle East expert at the Hoover Institute, a conservative US think tank, asserted that budding crisis "is all about China."

"Beijing has spent billions of dollars building Iran into a structural asset," Riboua wrote in a report she penned just days after Trump and his Israeli wing-man Prime Minister Benjamin Netanyahu began the aerial bombing campaign. "By striking Iran directly, the Trump administration is dismantling – whether by design or by consequence – a pillar of China's regional architecture."

In that context, the tough-guy reputations of Trump and China's leader Xi Jinping are at stake. The two had already entered a kind of low-intensity World War III dance during which the United States had moved step by step to turn back what Trump considered unacceptable Chinese inroads into areas important to US security.

He first sent commandoes into Caracas, the capital of Venezuela, to nab President Nicolas Maduro and spirit him off to New York to face trial on drug trafficking charges. Maduro sold petroleum to China and in return bought military equipment.