Protests Build Across the Country Against Trump's Immigration Order The president says order is about "terror and keeping our country safe."

 -- President Trump defended his executive order restricting the entry into the U.S. of people from seven Muslim-dominated countries, saying the move was not about religion but about keeping the country safe, but administration officials appeared to backtrack on the scope of the order, even as demonstrators gathered across the U.S. to protest.

Massive crowds packed Boston's Copley Square, Battery Park in New York City and outside the White House, and public areas in other cities, with demonstrations also held at airports from coast to coast to protest the order, which suspended immigration from countries with ties to terror -- Syria, Yemen, Sudan, Somalia, Iraq, Iran and Libya -- for 90 days. The order also indefinitely suspends Syrian refugees from entering the U.S.

Trump said in a statement released today that the countries chosen for what he called the "extreme vetting" of the order had been "identified by the Obama administration as sources of terror."

"To be clear, this is not a Muslim ban, as the media is falsely reporting. This is not about religion - this is about terror and keeping our country safe," the statement reads.

The administration, however, appeared to backtrack on one element of the order, saying late today that green card holders from those seven countries were not barred from re-entering the U.S., whereas earlier the administration had indicated they were.

"In applying the provisions of the president's executive order, I hereby deem the entry of lawful permanent residents to be in the national interest," Homeland Security Secretary John Kelly said in a statement today. "Accordingly, absent the receipt of significant derogatory information indicating a serious threat to public safety and welfare, lawful permanent resident status will be a dispositive factor in our case-by-case determinations."

A senior administration official confirmed this evening that legal permanent U.S. residents are exempt from the executive order. The official said the people who were set aside for additional screening were a "fractional marginal minuscule percentage" of travelers and said it is not an injury for green card and visa holders to be subject to additional screening.

The order has been criticized by Democratic elected officials and 16 attorneys general released a statement condemning the order as unconstitutional.

"We are confident that the Executive Order will ultimately be struck down by the courts. In the meantime, we are committed to working to ensure that as few people as possible suffer from the chaotic situation that it has created," said the statement, issued jointly by attorneys general of California, Connecticut, the District of Columbia, Hawaii, Illinois, Iowa, Maine, Maryland, Massachusetts, New Mexico, New York, Oregon, Pennsylvania, Vermont, Virginia and Washington.

A number of Republicans have also criticized the order, including Sens. John McCain and Lindsey Graham, who issued a joint statement today.

"It is clear from the confusion at our airports across the nation that President Trump’s executive order was not properly vetted," the senators said. "We are particularly concerned by reports that this order went into effect with little to no consultation with the Departments of State, Defense, Justice, and Homeland Security.

"Such a hasty process risks harmful results," the statement said. "Ultimately, we fear this executive order will become a self-inflicted wound in the fight against terrorism ... Our most important allies in the fight against ISIL are the vast majority of Muslims who reject its apocalyptic ideology of hatred."

Protesters marched along Pennsylvania Avenue toward the Capitol this afternoon, chanting, "No hate, no fear. Refugees are welcome here," and "No Ban. No wall."

According to immigrant and refugee advocacy groups, a number of people were being held today at airports across the country with some facing imminent deportation despite the stay on deportations issued by the U.S. District Court for the Eastern District of New York.

Among the people held after the ruling, according to Becca Heller, the director of the International Refugee Assistance Project, were: A 2-year-old U.S. citizen with green card-holding parents and a 66-year-old woman traveling from Iraq to visit her son, an active-duty U.S. service member who flew up to North Carolina to help her. A lot of people were being handcuffed, Heller said.

In one dramatic case late last night, an Iranian Fulbright scholar whose friends were waiting for her at John F. Kennedy International Airport in New York was forced to board a Ukraine International Airlines flight just before midnight -– hours after a federal court in Brooklyn issued a stay on the order, according to Heller. Only after high-level intervention did the plane turn around on the tarmac and let the woman deplane, Heller said.

The International Refugee Assistance Project encouraged anyone with a green card to reroute their flight through Boston if they don't want to be detained, after a ruling there said people couldn’t be deported or detained. The New York ruling said people couldn't be deported, but it allowed detention.

The advocates and lawyers said the haphazard implementation of the order has resulted in what Heller called "rogue" Customs and Border Protection officers pressuring green card holders to cancel them. She said that CBP officers repeatedly told them they were awaiting more information from Washington; finally, they stopped talking and "told us to just call President Trump," Heller said.

The groups said they're examining rulings in Boston, New York, and Virginia, to see whether there is overlap and whether they complement each other, and determine whether the rulings applied nationwide. In the case of the New York ruling, they said that the order did, but in the case of Boston, it was unclear, as it appeared it would, although it contained local references.

Thousands of attorneys have turned out en masse across the country, they said, including more than 4,000 people who signed up to help with the IRAP and many more showing up own their own, too. The executive director of the National Immigration Law Center said about 2,000 lawyers had formed a group dedicated to providing support on a regular basis.

Protesters at airports across the country reacted with jubilation Saturday night at the news that in response to a legal challenge issued by the ACLU a federal court in Brooklyn had granted an emergency stay on the president's executive order that bans immigration from Syria, Yemen, Sudan, Somalia, Iraq, Iran and Libya.

Following the court's decision, the Department of Homeland Security said in a press release that it "will continue to enforce all of the president’s Executive Orders in a manner that ensures the safety and security of the American people."

The statement noted that Trump's executive orders remain "in place," despite the emergency stay.

"The president's Executive Orders remain in place -- prohibited travel will remain prohibited, and the U.S. government retains its right to revoke visas at any time if required for national security or public safety," the release said.

The ACLU contended that the stay applied nationally to all cases, but that was not necessarily clear from the ruling, and an atmosphere of confusion still surrounds the orders, and how they will be applied going forward.

Today, the spontaneous protests that were sparked by news of travelers being detained were expected to continue in a more planned fashion at airports across the country.

The protests started Saturday at John F. Kennedy International Airport, where hundreds of people chanted "No hate, no fear, refugees are welcome here," angered at the detention of a number of people arriving from the countries listed in Trump's order, including the two Iraqi men whose cases were taken by the ACLU.

As the day went on, the protests spread to other major airports like Washington Dulles International Airport and Los Angeles International Airport.

The two Iraqis who were detained at JFK were both released later in the day, drawing widespread media attention.

One of the men, Hameed Jhalid Darweesh, expressed his gratitude for those who supported him while he was detained.

"America is the land of freedom," Darweesh said. "The land of freedom, the land of the rights. This is what brought me to come here, and I'm very thankful."

Neither Darweesh nor the other Iraqi were technically refugees according to the definition in the president's executive order at the time of their detention, but appear to have come to the U.S. on visas, a Trump administration official told ABC News.

A senior Department of Homeland Security official said that 375 travelers were affected by the executive order Saturday at airports across the country.

Within that group, 109 people were in transit and then denied entry to the U.S., 173 were denied entry to the U.S. before boarding their flights in a foreign port, and 81 were granted waivers because of their legal permanent resident or special immigrant visa status.

The number of people being held at U.S. airports is expected to dwindle today, but passengers at airports across the world may be kept from boarding flights to the U.S.

Trump said the executive order was part of a vetting plan to prevent "radical Islamic terrorists" from reaching American soil.

The seven-page document calls for an immediate suspension of immigration from countries with ties to terror -- Syria, Yemen, Sudan, Somalia, Iraq, Iran and Libya -- for a time period of 90 days. But none of the countries on the list have had anything to do with terror incidents on U.S. soil since the 9/11 attacks, and Saudi Arabia -- where 15 of the 9/11 hijackers were from -- is not included.

It also calls for the complete suspension of Syrian refugees for an indefinite period. It also calls on the secretary of state to suspend the entire U.S program for admitting refugees for 120 days while authorities review the application and adjudication process.

White House spokesman Sean Spicer said today on "This Week" that the seven countries had been identified by the Obama administration as needing further scrutiny, and said other countries could be added to the list at a later date.

ABC News' Benjamin Stein, David Caplan, Matt Foster, Aaron Katersky and Jack Date contributed to this report.