U.S. stock-index benchmark opened firmly lower to kick off the week, as trade-war fears dogged global markets. The Dow Jones Industrial Average slumped 263 points, or 1.1%, at 24,835, the S&P 500 index retreated by 0.8% at 2,757, and the Nasdaq Composite Index gave up 0.9% at 7,676. Markets were fixated on how trade-policy disputes the U.S. and China. President Donald Trump on Friday announced tariffs on $50 billion worth of Chinese imports, and Beijing retaliated by targeting high-value American exports. In corporate news, shares of Tesla Inc. were in focus after CEO of the electric-car maker Elon Musk showed off the company's newest production line.