US Secretary of State Mike Pompeo claimed on Thursday that the diplomatic status of the father of Huda Muthana, who was born in the US and joined the Islamic State group in 2014, means she is not a US citizen. The US has barred Muthana from returning.
"She may have been born here," Pompeo told NBC's "Today" show.
"She is not a US citizen, nor is she entitled to US citizenship."
The 24-year old who was born in New Jersey has urged the US to accept her return, saying she "deeply regrets" travelling to Syria to join the Islamic State group.
The decision, made under orders of President Donald Trump, is highly unusual, and contrasts with Trump's call on European countries to repatriate citizens who joined the Islamic State group.
The United States grants citizenship to virtually everyone born on its soil. The Constitution's 14th Amendment, however, contains a clause which exempts the children of foreign diplomats.
Pompeo has claimed that Muthana is not a US citizen as her father, Ahmed Ali Muthana, was a Yemeni diplomat at the time of her birth.
Hassan Shibly, Muthana's lawyer, told AFP that her father ceased working as a diplomat months before her birth.
Shibly provided Buzzfeed News with a letter from the US Mission to the United Nations stating Muthana's father left his diplomatic post one month before her birth.
Her father's lack of diplomatic status at the time should have given Muthana birthright citizenship.
Muthana apparently traveled to Syria under a US passport. She secretly renewed her passport before leaving home, her father told Buzzfeed News in 2015.
Muthana posted a photo of four women holding passports on Twitter in 2014 shortly after she arrived in Islamic State-held territory. A US passport was featured in the photo among passports of other nationalities.
"Bonfire soon, no need for these anymore," the post said.
Muthana is currently in al-Hawl camp in northern Syria under the custody of the US-allied Syrian Democratic Forces (SDF), along with her 18-month-old son.
"I thought I was doing things correctly for the sake of God," she told The Guardian on Sunday.
"I look back now and I think I was very arrogant…. I was brainwashed once and my friends are still brainwashed."
Muthana has pleaded with the United States to allow her to return and has said she is willing to face prosecution.
The denial of Muthana's citizenship could face serious legal challenges because it is extremely difficult for the United States to strip someone of their citizenship, as the UK has done with several prominent suspected Islamic State members, most recently Shamima Begum.