The largest exchange-traded fund to track Mexico's equity market fell sharply Friday, after U.S. President Donald Trump threatened to place escalating tariffs on all Mexican imports in an effort to force the country to slow the flow of Central American asylum seekers to the southern U.S. border. The iShares MSCI Mexico ETF /zigman2/quotes/203022585/composite EWW -0.27% fell 4.4% but was off initial lows. The ETF traded as low as $42.14, its lowest since March 14. The Mexican peso was off nearly 3% versus the U.S. dollar /zigman2/quotes/210561814/realtime/sampled USDMXN -0.1852% . The tariff threat rattled global markets, with investors already nervous about global growth prospects in part due to the continued U.S.-China trade battle. U.S. stocks traded sharply lower, with the S&P 500 /zigman2/quotes/210599714/realtime SPX +0.63% off 1.3%. The Dow Jones Industrial Average /zigman2/quotes/210598065/realtime DJIA +0.50% dropped more than 300 points, or 1.2%, to 24,865.