Chinese President Xi Jinping called for normal passage of ships through the Strait of Hormuz to be maintained, in a phone call on Monday with Saudi Arabia’s Crown Prince Mohammed bin Salman held as Beijing steps up efforts to help end US-Israel war against Iran.

China is concerned over renewed instability around the strategic waterway, as a US-Iran ceasefire came under fresh strain after the US seized an Iranian cargo ship and Tehran signalled it would not join new peace talks for now.

China is the main buyer of Iranian crude. Iran has largely closed the strait to ships other than its own since the US and Israel launched the war in February, while Washington has imposed a blockade of Iranian ships since last week.

China advocates an immediate and comprehensive ceasefire, and insists on resolving conflicts in the Middle East through political and diplomatic channels, state news agency Xinhua cited Xi as saying. “The Strait of Hormuz should remain open to normal passage, as this serves the common interests of regional countries and the international community,” he told the Saudi leader.

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Worries have mounted over the survival of the ceasefire between Washington and Tehran after the US seizure of the Iranian vessel. Trump had credited Beijing with helping to get Iran to the previous negotiations with the US in Pakistan.

The Chinese foreign ministry on Monday expressed concerns over the “forced interception” by the US of the Iranian ship, while urging relevant sides to abide by the ceasefire agreement.

Xi’s call with the Saudi crown prince followed a meeting in Beijing last week with the crown prince of Abu Dhabi, when Xi urged adherence to international law.

He also told the Saudi crown prince that China supports countries in the Middle East in “taking their future and destiny into their own hands, and promoting long-term regional stability and peace”.