Fears of an escalating feud between the U.S. and Iran have mounted since two oil tankers were attacked near the Strait of Hormuz last Thursday, and China’s top diplomat is warning against opening “Pandora’s box” in the Middle East as the U.S. sends more troops to the region.

The United States has officially blamed Iran for the attacks in one of the world’s most crucial waterways, the strait, where about one-third of the world’s oil supply travels out of the Middle East. Iran has previously threatened to blockade the strait, driving up the cost of oil across the world.

U.S. President Donald Trump said the strait would “not be closed for long” if that were to happen.

Iran has denied involvement and said Monday it would soon breach limits on how much enriched uranium it can stockpile according to the Iran nuclear agreement signed in 2015, which the U.S. pulled out of soon after Trump became president.

Since the tanker attacks, the U.S. has announced it is sending an additional 1,000 troops to the Middle East for defensive purposes, according to U.S. Defense Secretary Patrick Shanahan.

The Pentagon also released about a dozen photos on Monday that purportedly show an Iranian Islamic Revolutionary Guard Corps removing a limpet mine from a ship that did not explode.

“It is the assessment of the U.S. government that Iran is responsible for today’s attacks in the Gulf of Oman,” Secretary of State Mike Pompeo said last Thursday. Trump also put the blame squarely on Iran during an appearance on “Fox & Friends” last Friday.

Chinese State Councilor Wang Yi said the U.S. should not use “extreme pressure” to resolve the issues with Iran, according to a Reuters report, adding he is “of course very concerned” about further escalation and urged everyone to remain calm.

“We call on all sides to remain rational and exercise restraint, and not take any escalatory actions that irritate regional tensions, and not open a Pandora’s box,” he said. “In particular, the U.S. side should alter its extreme pressure methods. Any unilateral behavior has no basis in international law. Not only will it not resolve the problem, it will only create an even greater crisis.”

Wang also urged the U.S. to rejoin the Iran nuclear deal.

“We understand that relevant parties may have different concerns but first of all the comprehensive nuclear deal should be properly implemented,” he added. “We hope that Iran is cautious with its decision making, and does not lightly abandon this agreement.”

China is of course in an ongoing trade war with the U.S., and it has close energy ties to Iran. Beijing has been angered by U.S. sanctions that have prevented anyone from buying Iranian oil, including Chinese companies.

Trump has asked Iran to negotiate so the sides can work on a new nuclear arms deal.

“We want to get them back at the table, if they want to go back,” Trump said.

“I’m ready when they are, but whenever they’re ready, it’s OK. And in the meantime, I’m in no rush.”

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