 -- Congressman and Iraq War veteran Seth Moulton, D-Mass., said that President Donald Trump's executive order on immigration and refugees amounts to "a Muslim ban," despite the administration's assertions that the order aims solely to keep the country safe.

"What he's doing with this Muslim ban just is so wrong and un-American, you see why so many Americans across the country are rising up against it," the Democratic representative told ABC News' Martha Raddatz on "This Week."

When Raddatz noted, "They will tell you again and again, it is not a Muslim ban," Moulton replied, "There's no question what's going on here. We're not stupid. We see what Trump is up to."

On Saturday, Moulton tweeted to President Trump: "Your #MuslimBan is completely at odds with our most fundamental value: freedom. I'm ashamed that you are our president."

Moulton also said he believes that Trump's new defense secretary, ret. Gen. James Mattis, does not support the executive order. The order signed Friday immediately suspends immigration from seven predominantly Muslim countries in the Middle East and Africa -- Syria, Yemen, Sudan, Somalia, Iraq, Iran and Libya -- for 90 days. It also ends for 120 days the entry of any refugees into the U.S., and indefinitely suspends the entry of Syrian refugees.

"You know, I worked for Gen. Mattis. I know him," said Moulton, who as a lieutenant in the U.S. Marines served four tours in Iraq, including two as special assistant to Gen. David Petraeus. Moulton also worked to gain asylum in the U.S. for an Iraqi interpreter who risked his life working with Moulton and fellow U.S. service members.

"There is no way in hell that he is supportive of this," the congressman said of Mattis. "He relied on translators for his life, just like I did. He understands what it means to put your life in the hands of an Iraqi or an Afghan. And he also knows that implicit in that is that they put their lives in our hands, as well, and now we're abandoning them."

Mattis along with Vice President Mike Pence stood at Trump's side when the president signed the order Friday.

Moulton added that he believes the executive order is an indication that Mattis and another former high-ranking military officer in the administration, ret. Gen. John Kelly, the new secretary of homeland security, "don't have a voice in the Trump administration, that Trump is just doing things for political gain, not in the best interests of our national security."

The Democratic Massachusetts representative predicted the executive order will be used by terror groups as a recruiting tool and that it won't make the U.S. safer.

"It's fundamentally un-American, and it's also making America less safe. And that's something that Americans need to understand today, is that what Trump is doing is harming our national security. It will incite attacks against us. ISIS is already using this ban as propaganda. And it will prevent us from being able to get the allies that are so critical in our war against terror," Moulton said on "This Week."