All migrants detained overnight at Philadelphia International Airport under President Trump's executive order banning certain refugees and immigrants from entering the country were released Sunday, as continued protests drew thousands of demonstrators and opprobrium from a growing list of elected officials.

Gov. Wolf -- meeting in Center City with family members of six Christian Syrian immigrants who were sent back overseas Saturday despite having valid visas -- apologized and called the advent of the president's travel ban "a dark day for all of us."

"As Pennsylvanians and as Americans, this is not who we are," he said. "Pennsylvania is a place of welcome, not a place of oppression."

Ghassan Assali, an Allentown dentist and relative of the Syrian migrants, went further at a hastily called news conference Sunday afternoon.

"This is not American," he said. "This is more like ISIS."

Assali's six relatives were already on a return flight to Doha, Qatar Saturday night when a federal court in New York issued a temporary stay to Trump's order, which suspended entry of all refugees and migrants from seven predominantly Muslim countries for a period of months. Ghassan Assali said that his relatives had been trying to get here for 13 years.

"Their visas have been canceled," said Jonathan Grode, one of the lawyers for the family, "but we are trying to seek relief so that they do not have to start the process over again."

Four other immigrants, however, remained in custody in Philadelphia for hours Saturday and were prevented from contacting family members before they were admitted into the country and released early Sunday, said Mary Catherine Roper, legal director for the ACLU of Pennsylvania.

One woman, a U.S. citizen, spent most of Saturday in the U.S. Border Patrol's offices with her children after customs officials stopped her husband, fearing that if she left she would lose track of his status. That man was released late Saturday night.

Two other men — one from an African nation, the other, the spouse of a former translator for U.S. military forces in Iraq — were allowed to board domestic flights early Sunday to continue to other U.S. cities.

The fourth detainee -- a woman whose country of origin was not immediately available -- was also let go, though it was not clear whether Philadelphia was her final destination or if she was traveling elsewhere.

Their release came after a late-night bout of legal wrangling in Philadelphia that stretched into the early hours and a chaotic Saturday that brought about 200 demonstrators to the airport's international arrivals terminal.

Even as demonstrators packed the terminal chanting "Let them in," lawyers with the ACLU of Pennsylvania and other civil rights organizations were negotiating behind the scenes with the U.S. Attorney's Office in Philadelphia over if the stay to Trump's order issued by U.S. District Court Judge Ann M. Donnelly in Brooklyn applied to those migrants held locally.

Lawyers on both sides of the issue described a late-night teleconference with U.S. District Judge C. Darnell Jones II, who left a party he was attending Saturday night to oversee the discussions. An agreement was reached just after midnight, they said.

"We had petitions prepared, but the U.S. Attorney's Office agreed with everything we were seeking, so they were never actually filed," said Molly Tack-Hooper, a staff attorney at the ACLU.

Another, much larger protest erupted at the international terminal Sunday afternoon, with more than 4,000 participants, including U.S. Rep. Bob Brady (D., Philadelphia),  flooding the baggage claim areas and the surrounding streets.

"We need this," Brady said. "We need these voices."

Bruce Wright of Glassboro, white-haired and carrying a poster embellished with a peace sign and declaring he was from the "Woodstock generation," said he was "horrified by what is happening to my country."

"This is NOT the America I remember," his sign said. "Resist."

While only three people were detained in Philadelphia Saturday night, it remained unclear how many more might have been turned away and boarded other flights out of the country Saturday, said Tack-Hooper.

Assali, the Allentown dentist, said when he received a call from the airport telling him that his two brothers, their wives and two teenage children had been put on a plane and flown back overseas, he initially thought it was a prank.

Speaking Sunday, Assali said their move to Allentown had been in the works since 2003 and all of them had migrant visas and were approved for green cards.

His brothers and their families had returned to Damascus by Sunday afternoon, though it was not clear when they might attempt another return trip to the United States, Assali's wife, Sarmad, said.

"We've lived every day by the book, by the rules," she said. "They don't deserve this, and we don't deserve this. … If ISIS catches them [in Syria,] they are not safe."

Of those released Sunday, one -- Ahmed Al Janabi -- was on his way to reunite with his family, which had moved to Michigan after receiving threats in their native country because of his wife's work with the U.S. military in Iraq.

Al Janabi's wife, Shahad Keffah, brought their children over after receiving special immigrant visas last year. Her husband's move had been delayed until Saturday because his passport had expired and it took six months to renew.

The family had waited three years and went through seven rounds of background checks before receiving their visas last year, said the ACLU's Tack-Hooper.

Still, their futures remain uncertain.

The stay issued Saturday in New York offered only a stopgap measure until the legal challenge to Trump's travel ban receives a full hearing in federal court, currently scheduled for Feb. 24.

Until then, said lawyers who filed the suit, visa-holding migrants and certified refugees who manage to reach America are protected – nationwide -- by the Judge Donnelly's temporary restraining order.

Pennsylvania Attorney General Josh Shapiro and his counterparts from 16 other states also vowed in a joint statement Sunday afternoon to defend the rights of migrants arriving lawfully in the country.

"As the chief legal officers for over 131 million Americans and foreign residents of our states, we … will work together to ensure the federal government obeys the Constitution, respects our history as a nation of immigrants, and does not unlawfully target anyone because of their national origin or faith.

"Religious liberty has been, and always will be, a bedrock principle of our country and no president can change that truth."