A U.S. institute tracking Iran’s military program says recent satellite images show further major alterations of a military site that the U.N atomic agency suspects may have been used in trying to develop nuclear arms.

The most recent imagery from satellite company Digital Globe is from Aug. 13. It was seen by The Associated Press ahead of publication by the Institute for Science and International Security.

It shows what ISIS says is progressive asphalting of a part of the Parchin complex that the International Atomic Energy Agency says was possibly used to test conventional explosive triggers for a nuclear blast.

Iran has refused the IAEA access and dismisses suggestions that the asphalting and other work at the site are an attempt to hide traces of nuclear weapons work.

(AP)