A senior U.S. defense official has explained why the American military keeps returning to bomb the same Iranian targets it has already struck repeatedly since the conflict began in late February, according to Fox News national security correspondent Jennifer Griffin.

In a post on social media, Griffin said she pressed the official on why the U.S. has had to go back and restrike sites that have been hit multiple times since February 28, when the war began. The answer, she reported, was that Iran has rebuilt its air defense and missile systems along the Strait of Hormuz in the months since the U.S. bombing campaign wound down on April 7.

That reconstitution, the source told Griffin, is why the military is now having to strike areas like Qeshm Island and Sirik that it had already targeted in the past.

"In the time since the cease fire on 7 April, Iran has reconstituted — thus the targets around the Strait of Hormuz," the official told Griffin.

The official acknowledged the scale of the damage already inflicted on Iranian positions while making clear that Tehran has adapted.

"There is a LOT that is damaged… a LOT… but they moved things around," the source said.