U.S. stocks tumbled, sending the S&P 500 Index to its biggest weekly loss in more than two years, on concern that a trade war and higher borrowing rates could throttle global growth. Oil surged on speculation sanctions on Iran will be re-imposed.

The Dow Jones Industrial Average slumped for a third consecutive day, led by losses in companies as diverse as 3M Co. to Goldman Sachs Group Inc. The S&P 500 dropped to its lowest since the volatility-fueled meltdown in early February. Gold rallied and Treasury yields declined as investors sought safe havens.

Global markets were caught in a risk-off mode after China announced retaliation against President Donald Trump's proposed tariffs announced Thursday. China's ambassador to the U.S. wouldn't rule out the possibility of the Asian nation scaling back purchases of Treasuries in response to the tariffs.

It's been a miserable week for higher-risk markets globally, as a trade war edged closer, the tech sector was roiled by Facebook Inc.'s privacy scandal and data showed European growth sputtering. Traders had already been bracing for the possibility of slowing expansion as the Federal Reserve reiterated its commitment to further interest-rate increases after Wednesday's hike.

"There is a tug of war between Fed tightening, fiscal stimulus, strong earning but slowing sales and now tariffs and potential trade wars," said Jason Browne, chief investment strategist at FundX Investment Group.

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Adding to the image of the ascendance of the "America first" faction, Trump said he is replacing White House National Security Adviser H.R. McMaster with John Bolton, a controversial foreign-affairs specialist whom the U.S. Senate declined to confirm as President George W. Bush's ambassador to the United Nations.

These are the main moves in markets:

- The S&P 500 Index dropped 1.9 percent as of 3:49 p.m. New York time, while the Dow Jones Industrial Average erased 1.5 percent and the Nasdaq Composite Index dropped 2.2 percent.

- The Stoxx Europe 600 Index fell 0.9 percent and the MSCI Asia Pacific Index tumbled 2.6 percent.

- The U.K.'s FTSE 100 Index slipped 0.4 percent, after touching the lowest in more than 15 months.

- The MSCI Emerging Market Index fell 2 percent.

- The Bloomberg Dollar Spot Index fell 0.3 percent.

- The euro rose 0.5 percent to $1.2362, the strongest in more than a week.

- The British pound increased 0.3 percent to $1.4137.

- The Japanese yen advanced 0.5 percent to 104.78 per dollar, the strongest in more than 16 months.

- The yield on 10-year Treasuries fell one basis point to 2.82 percent.

- Germany's 10-year yield was little changed at 0.53 percent.

- Britain's 10-year yield gained one basis points to 1.44 percent.

- West Texas Intermediate crude increased 2.5 percent to $65.89 a barrel.

- Gold increased 1.4 percent to $1,348.21 an ounce, the highest in more than a month.

- With assistance from Robert Brand