European and US stock markets swooned into the red Monday on downbeat US economic data and news of fresh US tariffs against Argentina and Brazil.
Asian markets had been cheered earlier in the day by a surprise jump in Chinese factory activity, but the party ended with a tweet by US President Donald Trump.
Trump tweeted that owing to unfair policies by Brazil and Argentina, he would reinstate tariffs on steel and aluminium from those countries.
"It doesn't take a genius to guess how investors reacted," said analyst Connor Campbell at Spreadex.
"Reversing their early gains, the eurozone indices all sank into the red, joined by an irritated Dow Jones," he noted.
Trade-related concern was also stoked by China's Global Times newspaper, which said Beijing wanted all US tariffs rolled back as part of a mini deal, a move observers said Washington is unlikely to agree to.
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On Saturday, China said its manufacturing sector expanded in November for the first time in seven months, providing a boost to investors looking for signs of optimism in the world's second biggest economy.
Another survey Monday of smaller firms also showed a better-than-expected pick-up in factory activity.
On oil markets, crude prices came back from sharp losses last week after Iraq said top producers might announce an output cut soon.
On foreign exchange markets, the euro rose against the dollar after a survey revealed that the US manufacturing sector has contracted for a fourth straight month, which put more pressure on eurozone stocks because many companies would be hampered by the stronger single currency.
Some analysts had already raised concerns about an article in the Communist Party-linked Global Times, which tweeted that the government wants levies imposed on China to be removed as the US talks continue. It also said leaders wanted tariffs lined up for December 15 to be taken off the table.
But OANDA senior market analyst Jeffrey Halley said: "It is hard to see the US swallowing a very bitter trade pill like that; it would, in effect, remove all of the US's leverage in the far more difficult comprehensive trade negotiations to come."