U.S. markets slumped early Tuesday after Chinese sanctions against the U.S. subsidiaries of a major South Korean shipbuilder shook a fragile sense of calm over trade tensions with Washington.

Futures for the S&P 500 lost 1% before the opening bell, while futures for the Dow Jones Industrial Average slid 0.6%. Nasdaq futures tumbled 1.3% as a broad of swath of technology companies saw their shares slide.

China’s Commerce Ministry said Tuesday it was banning dealings by Chinese companies with five subsidiaries of South Korean shipbuilder Hanwha Ocean, swiping at President Donald Trump’s efforts to rebuild the industry in America.

“China just weaponized shipbuilding,” said Kun Cao, deputy chief executive at consulting firm Reddal. “Beijing is signaling it will hit third-country f

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