It took place in the Parchin area in the southeast of Tehran due to "leaking gas tanks," Iran's defense ministry said on Friday, adding there were no casualties. Parchin is a site suspected of having hosted conventional explosion tests applicable to nuclear power, which the Islamic republic denies. It had come under scrutiny from the U.N.'s International Atomic Energy Agency in 2015. Iran had refused the IAEA access to the site because of the nature of its work, but the agency's then-chief, the late Yukiya Amano, paid a visit there.