An Alabama woman who left home to join the Islamic State group in Syria is not a U.S. citizen and will not be allowed to return to the United States, Secretary of State Mike Pompeo said on Wednesday.

In a brief statement that gave no details as to how the determination was reached, Pompeo said Muthana, who says she made a mistake in joining the group and now wants to return with her 18-month-old son, has no "legal basis" to claim American citizenship.

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

Muthana's status had been considered by lawyers from the departments of State and Justice since her case arose, according to one U.S. official who was not authorized to discuss the matter publicly and spoke on condition of anonymity. The official would not elaborate but said Pompeo's statement was based on the lawyers' conclusions.

An attorney for the woman's family, Hassan Shibly, said the administration's position is based on a "complicated" interpretation of the law involving her father.

"They're claiming her dad was a diplomat when she was born, which, in fact, he wasn't," Shibly told The Associated Press.

Muthana was born in 1994 in Hackensack, New Jersey, the lawyer said.

Most people born in the United States are accorded so-called birthright citizenship but there are exceptions.

Under the Immigration and Nationality Act, a person born in the U.S. to a foreign diplomatic officer is not subject to U.S. law and is not automatically considered a U.S. citizen at birth.

The 24-year-old, who joined the Islamic State after becoming radicalized, says she regrets aligning herself with the terrorist organization and wants to return to the United States, Shibly said on Tuesday. He said Muthana is putting herself at risk by speaking out against ISIS from a refugee camp where she has lived since fleeing the group a few weeks ago.

Muthana, who dodged sniper fire and roadside bombs to escape, is ready to pay the penalty for her actions but wants freedom and safety for the son she had with one of two IS fighters she wed, he said. Both men were killed in combat.

In a handwritten letter released by Shibly, Muthana wrote that she made "a big mistake" by rejecting her family and friends in the United States to join the Islamic State.

"During my years in Syria I would see and experience a way of life and the terrible effects of war which changed me," she wrote.

After fleeing her home in suburban Birmingham in late 2014 and resurfacing in Syria, Muthana used social media to advocate violence against the United States. In the letter, Muthana wrote that she didn't understand the importance of freedoms provided by the United States at the time.

"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," said the letter.

Shibly said Muthana was brainwashed online before she left Alabama and now could have valuable intelligence for U.S. forces, but he said the FBI didn't seem interested in retrieving her from the refugee camp where she is living with her son.

Muthana's father would welcome the woman back, Shibly said, but she is not on speaking terms with her mother.

Ashfaq Taufique, who knows Muthana's family and is president of the Birmingham Islamic Society, said the woman could be a valuable resource for teaching young people about the dangers of online radicalization were she allowed to return to the United States.

"Her coming back could be a very positive thing for our community and our country," Taufique said.