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For the first time since the eurozone crisis, the world's biggest wealth manager is bearish on stocks.

In a note to investors, UBS Wealth Management Chief Investment Officer Mark Haefele said that the group, which manages more than $2.4 trillion, has shifted to an "underweight" recommendation on equities.

The bank advised its wealthy clients to lower the proportion of stocks in their portfolios following President Donald Trump's decision to raise tariffs on all exports from China by 5% last Friday.

Here's why: "The US-China trade dispute has escalated in recent days, raising the risk of a cycle of retaliation that undermines global growth and equities markets," Haefele said. "That justifies a reduction in risk in our portfolios in order to lower our exposure to an uncertain political environment."

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