An Alabama woman who left home to join the Islamic State group in Syria is not an American citizen and will not be allowed to return to the US, Mike Pompeo has said.

The Secretary of State said Hoda Muthana does not have a US passport or any legal basis to enter the country.

He said that she “will not be admitted to the United States”.

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Secretary of State Mike Pompeo said the woman who joined IS could not return to the US (Czarek Sokolowski/AP)

The 24-year old, who joined the Islamic State after becoming radicalised, says she regrets aligning herself with the terrorist organisation and wants to return to the US with her 18-month-old son.

Muthana’s status had been considered by lawyers from the departments of State and Justice since her case arose, according to a US official.

A lawyer 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,” Mr Shibly said.

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 US to a foreign diplomatic officer is not subject to US law and is not automatically considered a US citizen at birth.

Mr Shibly said Muthana is putting herself at risk by speaking out against Islamic State 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 Mr 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 did not 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.

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

Muthana’s father would welcome the woman back, Mr 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 radicalisation were she allowed to return to the United States.

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