The F.B.I. has arrested an American woman who federal prosecutors said had risen through the ranks of the Islamic State in Syria to become a battalion commander, training women and children to use assault rifles and suicide belts, the Justice Department disclosed on Saturday.

The woman, Allison Fluke-Ekren, 42, a former teacher from Kansas, was charged with providing material support to a terrorist organization. The circumstances of her capture in Syria were not immediately known, but the F.B.I. flew her to Virginia on Friday to face prosecution.

Prosecutors described Ms. Fluke-Ekren as playing an unusually outsized role in the Islamic State as a woman and an American. Charges against American women involved with the Islamic State have been rare.

Investigators said Ms. Fluke-Ekren was smuggled into Syria in 2012 from Libya. She traveled to the country, according to one witness, because she wanted to wage “violent jihad,” Raj Parekh, a federal prosecutor, wrote in a detention memo that was made public on Saturday.

According to a criminal complaint that was filed in 2019, a witness told the F.B.I. that Ms. Fluke-Ekren and her husband brought $15,000 to Syria to buy weapons. Her husband, the witness said, eventually rose to be the commander of all snipers in Syria in 2014. He later died in an airstrike while conducting a terrorist attack on behalf of the Islamic State, investigators said. Ms. Fluke-Ekren met her husband in the United States, according to court documents.

The same witness also told the F.B.I. that Ms. Fluke-Ekren had a plan in 2014 to attack a college in the United States using backpacks filled with explosives. Prosecutors did not reveal which college she had wanted to target. The criminal complaint said her plan was presented to Abu Bakr al-Baghdadi, the leader of the Islamic State at the time, who approved it for funding. The witness said the attack was put on hold after Ms. Fluke-Ekren learned she was pregnant. Ms. Fluke-Ekren had multiple children, but it is not clear how many.

Prosecutors said Ms. Fluke-Ekren moved to Egypt in 2008, lived there for about three years and then traveled to Libya, where she stayed for about a year before sneaking into Syria. According to one witness, Ms. Fluke-Ekren departed Libya because another terrorist organization, Ansar al-Sharia, was no longer conducting attacks in that country and she wanted to wage violent jihad.

In his memo arguing to keep Ms. Fluke-Ekren behind bars while she awaits trial, Mr. Parekh said she had been a “fervent believer in the radical terrorist ideology of ISIS for many years.” The prosecutor said the government had numerous witnesses who were prepared to testify against her.

According to the detention memo, the mayor of the Syrian city of Raqqa, the Islamic State’s self-proclaimed capital, approved the opening of a military battalion to train women to help defend the city. Ms. Fluke-Ekren, investigators said, soon became the leader and organizer of it.

Witnesses said that Ms. Fluke-Ekren taught classes for members of the battalion, and on one occasion, a young child of hers was seen holding an assault rifle. One witness said that more than 100 women and girls had received training from Ms. Fluke-Ekren. She had hoped to create a cadre of suicide bombers that could infiltrate enemies’ positions, but the effort never materialized, according to the complaint.

Ms. Fluke-Ekren told another witness about her desire to attack a shopping mall using a remote-detonated vehicle full of explosives. The witness said she wanted to kill large numbers of people.

Court documents said that after the death of her husband, Ms. Fluke-Ekren married another Islamic State terrorist, a Bangladeshi man who specialized in drones and was working on a plan to drop chemical bombs from the air. He also died. She then married an Islamic State military leader who was responsible for the defense of Raqqa, a witness said.

A witness also said that Ms. Fluke-Ekren claimed to have tried to send a message to her family with the goal of tricking them into believing she was dead so the U.S. government would stop trying to find her. She told the witness that she never wanted to return to the United States and wanted to die a martyr in Syria.

Federal prosecutors in Virginia have mounted an aggressive effort to prosecute terrorists captured overseas. The cases can be extremely difficult because witnesses and other evidence can often only be found in war zones, as well as because of geopolitical considerations.

Last year, Mohammed Khalifa, a Saudi-born Canadian who traveled to Syria in 2013 and later joined the Islamic State, was brought to the United States and charged with providing material support to a terrorist organization that resulted in death. Mr. Khalifa provided the narration and translation for approximately 15 videos created and distributed by the Islamic State. He later pleaded guilty and faces life in prison.

Two British men, El Shafee Elsheikh and Alexanda Kotey, who were part of an ISIS cell of four Britons called “the Beatles,” were brought to the United States in 2020 to face charges. The group, which was given that nickname by its victims because of the accents of its members, kidnapped and abused more than two dozen hostages, including the American journalists James Foley and Steven J. Sotloff, both of whom were beheaded in propaganda videos.

Mr. Kotey pleaded guilty to his role in deaths of four Americans in Syria. He faces life in prison. Mr. Elsheikh has pleaded not guilty and awaits trial.