The S&P 500 opened the week lower as geopolitical tensions escalated following the US announcement of a naval blockade targeting Iran's shipping routes. President Trump's administration moved to restrict transit through the Strait of Hormuz—a critical chokepoint for global oil shipments—after failed negotiations with Tehran.

Two Iranian-linked vessels transited the strait hours before the blockade took effect, according to ship-tracking data. While overall traffic through the waterway has declined sharply, Iranian-affiliated ships continue navigating the route at near-normal levels, testing the boundaries of the new restrictions.

Market volatility spiked as traders weighed the potential for prolonged disruptions to energy shipments. The blockade threatens to squeeze global commodity flows at a time when supply chains remain fragile from prior geopolitical shocks.