What is Iran’s Pickaxe Mountain?

Donald Trump has threatened to strike Pickaxe Mountain, an underground nuclear-related complex near Iran's Natanz facility. Al Jazeera's Ava Warriner examines what is known about the site and what the threat suggests about Washington's earlier claims of victory. The site is located near the Natanz enrichment plant. The threat casts doubt on previous US assertions of success regarding Iran's nuclear program.