Iran is ringing two deeply buried tunnel complexes with a massive security perimeter linked to its main nuclear facility, a report said Wednesday, amid U.S. and Israeli threats of attack. The Institute for Science and International Security released its report based on recent satellite imagery as the U.

The United States and Iran are due to hold their second round of nuclear talks on Saturday, as what both sides are looking for in a deal begins to take shape.

That the talks are even happening represents a historic moment, given the decades of enmity between the two countries.