National Security Adviser H.R. McMaster on Sunday addressed President Trump’s decision last week to nix the Iran nuclear deal unless the rogue nation fully complies with the 2015 international pact, saying it’s not a “trustworthy regime” and that it has already “crossed the line several times.”

Trump on Friday accused Iran of violating the Obama-era deal. However, the president didn’t terminate it or re-impose sanctions. Instead, he told Congress to toughen the law that governs U.S. participation while calling on the other parties to fix a series of deficiencies.

“It's a weak deal that is being weakly monitored,” McMaster said on “Fox News Sunday.” “The president has made clear that he will not permit this deal to provide cover for what we know is a horrible regime to develop a nuclear weapon.”

McMaster also argued that other nations that signed the deal agree with Trump about the changes and that Iran will need to renegotiate.

“Our European allies already support much more rigorous reinforcement of [the deal] and more monitoring,” McMaster said.

The landmark deal, signed in July 2015, prevents Iran from building a nuclear bomb. Iran, along with the five permanent members of the U.N. Security Council – the United States, Britain, France, China and Russia – agreed that sanctions that were in place for years would be lifted. The deal means Iran can receive billions of dollars in funds that were previously frozen and allow its markets to be re-opened to foreign investors, according to reports.

“One of the real problems with this deal,” McMaster said, “is we can't really say with confidence that they [Iranian officials] are complying and we know from their behavior, probably in the region and their behavior within the agreement where they have walked up to the line, they have crossed the line several times in terms of the restrictions. This is not a trustworthy regime so much more comprehensive monitoring is in order.”

McMaster added that Trump is not yet ready to walk away from the deal, and is waiting to see if there is real change or the ability of Congress to address the issues regarding monitoring Iran and whether the country is complying with the agreement.