Explainer: Why U.S. threatens to strike Iran's Pickaxe Mountain?

CAIRO, July 23 (Xinhua) -- Tensions between Washington and Tehran have escalated in recent days, with Pickaxe Mountain -- a fortified site near Iran's Natanz enrichment facility -- emerging as the confrontation's new flashpoint. Threats from Washington to strike the fortified underground complex have widened the rift between the two sides, stoking fears of renewed instability across the Middle East.