WASHINGTON (TNND) — The United States had meticulously planned a potential strike on Iran's Fordo nuclear site for years, according to a former high-ranking U.S. official.

Former Middle East & North Africa Coordinator for the National Security Council Brian McGurk spoke to CNN after the strikes conducted on Iran early Sunday.

"You just can't leave Fordo, uh, untouched, and this operation, I know it well because we spent about 2 years, uh, refining it, making sure it's ready if a president ever needed it. I'm, I'm fairly confident it was successful," McGurk told the outlet.

McGurk also mentioned speaking with a senior administration official who felt the strike was very effective. Officials have clarified that this is not an expanded campaign against Iran, but rather a targeted action against its nuclear program.

The question now is how Iran will choose to respond.

McGurk suggested potential Iranian responses could fall into three categories: "We know them well, uh, missiles, militias and terrorism or hostage taking, uh, but I think we have, as I understand it. Uh, post sent a warning to Iran not to think about that. And if they do, we would have a counter trying to avoid going up that ladder."

President Trump has issued a warning to Iran not to retaliate.

Meanwhile, Iran's Supreme Leader warned earlier this week that a U.S. strike would be detrimental to the United States, though he did not provide specifics.