Calling former President Barack Obama's controversial Iran nuclear deal a "mistake," hoping President Donald Trump pulls out of it, former Sen. Joe Lieberman, I-Conn., ripped former Secretary of State John Kerry's lobbying for the deal with Iranians "inappropriate" and a potential violation of the Logan Act.

"John Kerry is not negotiating on behalf of the U.S. government, I hope everybody he's talking to knows that, but in my opinion what he's doing is inappropriate and he shouldn't be doing it," Lieberman told Fox News' "Sunday Morning Futures" Maria Bartiromo.

"Let's just take two former secretaries of state – Conde Rice, who opposes the Iran nuclear agreement [and] Hillary Clinton, who supported it – neither one of them is going around talking to the Iranians, to the Europeans, and trying to I guess convince them to not be affected by the current Trump administration.

"It's a duly elected administration, so I hope John Kerry stops."

Lieberman not only disagrees with Kerry's potentially illegal actions negotiating without the administration's consent, but he also agrees Trump's position so far.

"Well I'm encouraged by what the president has said so far, and I hope he does pull out," Lieberman told Bartiromo. "I give you the perspective of somebody who was in the Senate for 24 years, worked with people in both parties to put sanctions, economic pressure on Iran with a singular goal, which was to denuclearize Iran to stop their nuclear weapons development program.

"And what the Obama administration and our allies in Europe did was not that. It basically gave away all our leverage against them in return for a pause in their nuclear program – if they're keeping their word, which they don't have a good reputation for doing – and it gave them $100 billion which they've used to support terrorists and to spread their rule throughout the Middle East.

"So, it was a bad deal, a mistake for us. I think the president really has the power to correct that mistake, and I hope he does."