Major powers and Iran finessed how U.N. inspectors will get access to Iranian military sites in Tuesday's nuclear agreement, with a formula that gives the United Nations strong inspection powers while allowing Tehran to save face.

Deep in the deal's details is a procedure under which Iran would have to provide access to suspect sites, including at its military facilities, within 24 days. If Iran refused, it would face the possibility of U.N. sanctions being slapped back on it.

The procedure was crafted to ensure U.N. inspectors could get access to allay their suspicions about Iran's nuclear activities. But it does not explicitly force Iran to admit that its military sites could be open to foreign inspections, leaving some uncertainty over the access Iran will allow in practice.