U.S. stock markets closed lower on Thursday due to attacks on oil and gas infrastructure in Qatar and Iran, raising fears of energy supply disruptions and regional instability. The three major indices all ended in negative territory. The Standard and Poor's 500 slipped 18.20 points, or 0.27 percent, to close at 6,606.50, while the Dow Jones Industrial Average dropped 203.23 points to settle at 46,021.92. The tech-heavy NASDAQ Composite also saw declines, falling 61.73 points to end the session at 22,090.69. The most notable action was seen in the euro and sterling, both of which posted strong gains against the dollar. The US dollar also fell sharply against the Japanese yen (USDJPY) as investors sought the currency amid ongoing geopolitical tensions.