(Image source from: weigelbroadcasting.com)

President Donald Trump on Wednesday said he is barring a United States-born former Islamic State of Iraq and Syria (ISIS) propagandist from returning home, making the extremely unusual case that she is not a U.S. citizen.

The refusal to admit the 24-year-old Hoda Muthana comes just as he is calling on Europeans to repatriate their own ISIS fighters and will probably face legal challenges, with U.S. citizenship extremely difficult to lose.

Trump said on Twitter he has "instructed", Secretary of State Mike Pompeo "not to allow Hoda Muthana back into the country" - a break with usual U.S. protocol not to comment on individuals' immigration issues.

"Ms. Hoda Muthana is not a U.S. citizen and will not be admitted into the United States," Pompeo said in a terse statement.

"She does not have any legal basis, no valid U.S. passport, no right to a passport, nor any visa to travel to the United States," he added.

The U.S. In general grants citizenship to everyone born on its soil and the Alabama-raised Muthana is believed to have traveled to Syria on a U.S. passport.

But a U.S. official said a later investigation showed that she had not been entitled to her passport, adding: "Ms. Muthana's citizenship has not been revoked because she was never a citizen."

Muthana's father had been a diplomat from Yemen - and children of diplomats are not automatically given citizenship. Muthana's attorney, Hassan Shilby, showed a birth certificate that demonstrated she was born in New Jersey in 1994 and said her father had ceased being a diplomat "months and months" before her birth.

"She is a U.S. citizen. She had a valid passport. She may have broken the law and, if she has, she's willing to pay the price," Shilby told AFP at his office in Tampa.

He said Muthana wanted due process and was willing to go to prison if convicted.

"We cannot get to a point where we simply strip citizenship from those who break the law. That's not what America is about. We have one of the greatest legal systems in the world, and we have to abide by it.

Muthana, raised in a strict household in Hoover, Alabama, said she was brainwashed by social media messages and headed to Syria without her parents' knowledge in 2014.

Soon, Muthana posted on Twitter a picture of herself and three other women who appeared to torch their Western passports, including an American one.

She went on to post evocative calls on social media to kill Americans, lauding the pitiless extremist group ill-famed for its beheadings that for a time ruled vast swathes of Syria and Iraq.

But with the ISIS group down to its last stretch of land, Muthana said she has renounced extremism and wants to return home with her toddler son, born to one of her three jihadist husbands.

"To say that I regret my past words, any pain that I caused my family and any concerns I would cause my country would be hard for me to really express properly," she said in a handwritten note to her lawyer.

The decision by the U.S. on Muthana comes amid rising debate in Europe on the nationality of extremists. Britain recently revoked the citizenship of Shamina Begum, who likewise traveled to Syria and wants to return to her country of birth.

-Sowmya Sangam