They thought they were going out of town for a girls weekend.

Two 7-year-old girls from Minnesota checked into a Farmington Hills hotel with their mothers in February, court records show, thinking they were there for a "special" trip.

But instead of visiting the zoo or going shopping, the youngsters ended up in a doctor's office in Livonia, where a physician subjected them to what federal authorities are calling a "barbaric" and "horrifying" procedure: She cut their genitals as part of a religious and cultural practice that seeks to curb females' sexuality and continues in societies worldwide.

Related: How common is female genital mutilation in the US?

The girls were told to keep it secret, records show, but the FBI found out.

In what officials say is a first-of-its kind federal case targeting the practice of genital mutilation, Dr. Jumana Nagarwala, 44, of Northville was charged Thursday with mutilating the genitals of two girls, although authorities say they believe she has subjected numerous more girls to the procedure, including children in metro Detroit. Authorities would not comment on whether more charges are coming, but the case appears to be the tip of the iceberg if the FBI's words are any indication.

Related: Detroit doctor accused of genital mutilation on 7-year-old girls

"This investigation has identified other children who may have been victimized by Nagarwala," FBI agent Kevin Swanson wrote in an affidavit that was unsealed Thursday. "(Investigators) interviewed several minor girls in Michigan about FGM (female genital mutilation). In these interviews, multiple minor girls informed child protective services and forensic interviewers that procedures had been performed on their genitals by Nagarwala."

Nagarwala, an emergency room doctor at Henry Ford Hospital in Detroit and a U.S. citizen, appeared in U.S. District Court in Detroit on Thursday handcuffed and shackled, wearing a white headscarf, glasses and long white dress with colorful embroidery near her shackled feet. The defendant, who also speaks Gujarati — a language spoken in western India — will be locked up pending a detention hearing Monday, when a judge will determine whether to grant her bond or keep her jailed pending the outcome of her trial.

Two male family members were in the courtroom but said nothing to reporters. Her attorney, Shannon Smith of Bloomfield Hills, declined to comment.

Her employer, Henry Ford Health Systems, expressed concern about the allegations and said Nagarwala has been placed on administrative leave.

"We are shocked by the allegations," Henry Ford Health System spokesman David Olejarz said in statement, stressing: "The alleged criminal activity did not occur at any Henry Ford facility. We would never support or condone anything related to this practice."

Authorities would not disclose what religion the defendant practices, or what cultural group she is affiliated with — stating only that she is part of a religious and cultural community that's known to practice genital mutilation on girls. One Indian-American leader told the Free Press that female genital mutilation is not a Hindu practice.

In the U.S., genital mutilation qualifies as a criminal sexual act, as the intent of the procedure is considered to abuse, humiliate, harass or degrade.

The U.S. Attorney's Office says this is the first such criminal case in the country, with prosecutors relying on a federal law that criminalizes the practice of female genitalia mutilation, which is punishable by up to five years in prison. The doctor, however, could get 10 years to life in prison for another crime she was charged with: transportation of an individual with intent to engage in criminal sexual activity.

"The allegations detailed in today's criminal complaint are disturbing. The FBI, along with its law enforcement partners, are committed to doing whatever necessary to bring an end to this barbaric practice and to ensure no additional children fall victim to this procedure," Detroit's FBI chief, David Gelios, said.

Especially egregious, authorities said, is that the accused is a doctor who is supposed to help and heal people.

"Female genital mutilation constitutes a particularly brutal form of violence against women and girls. it is also a serious federal felony in the United States. The practice has no place in modern society, and those who perform (female genital mutilation) on minors will be held accountable under federal law," stated Acting U.S. Attorney Daniel Lemisch.

On Tuesday, authorities caught up with Nagarwala, who according to court records, volunteered to be interviewed by a Homeland Security agent and Michigan child protective services personnel. During her interview, she said that she is aware that female genitalia mutilation is illegal in the U.S., but denied ever performing the procedure on any children. She also said that she had no knowledge of the procedure being performed on anyone in her cultural community.

Nagarwala earned her medical degree from Johns Hopkins University in 1998, according to the Henry Ford Health Systems website. Her bio lists the languages she speaks as English and Gujarati, spoken by the Gujaratis, who hail from the western India state of Gujarat, the same ethnic area that Mahatma Gandhi came from.

According to an online petition at change.org, there's a movement in India to end female genital mutilation within a small Muslim sect known as Dawoodi Bohra. Gujarat is predominantly Hindu, but there are also significant populations of Muslims, Christians and Jains, according to a 2011 census.

For Sree Kamojjala, president of the Indian Association of Minnesota, the case of the Michigan doctor is both shocking and deplorable, he said, stressing that genital mutilation "is not a Hindu practice" or a condoned practice in India.

"What shocks me is I have never heard of this in India. ... It’s totally brutal. You can’t even think of your little girls going through this stuff. I don’t know what to say," Kamojjala said in a phone interview. "We as a community totally condemn these kinds of acts. I am really sorry to hear this. I can’t find words. It’s ridiculous.”

According to court documents, investigators relied on cell phone records and surveillance video to piece together the case against Nagarwala. It's unclear what led them to the doctor to begin with. According to the complaint, federal investigators at some point received a tip that Nagarwala had performed genital mutilation on two young girls in Livonia, so they followed up with an investigation.

First, they searched the doctor's phone records, which revealed a string of phone calls in February between the doctor and a Minnesota couple with a 7-year-old daughter. Then, with the help of cellular records and surveillance video, federal agents learned that a 7-year-old girl and her mother had traveled to metro Detroit on Feb. 3 and stayed at a Farmington Hills hotel along with another 7-year-old girl and her parent. The next day, they were back in Minnesota, phone records show. But while in metro Detroit, the girls visited Nagarwala at an unnamed Livonia clinic and underwent genital mutilation procedures, court records state.

A month after the visit to Detroit, both girls interviewed with a forensic expert with the FBI. One of the girls said that she thought she was coming to Detroit for a "special" girls trip, but after arriving at the hotel, she learned that she and the other girl had to go to the doctor because "our tummies hurt."

While at the doctor's office, a procedure "to get the germs out" of her was performed, the complaint stated. The girl was given a pad to wear and was told "not to talk about the procedure," the complaint said. A second girl told a similar story, telling the investigator that "her parents told her that the procedure is a secret, and that she is not supposed to talk about it."

On April 10 and 11, a medical doctor in Minnesota performed medical exams on both girls, pursuant to a search warrant. That doctor told the FBI that both girls' genitals were not normal in appearance and had been "altered or removed."

The parents of one of the girls were interviewed by Minnesota child protection services personnel and a federal agent. They said they took the girl to Detroit to see Nagarwala for a "cleansing" of extra skin, the complaint said.

According to the World Health Organization, female genital mutilation is an internationally recognized violation of human rights of girls and women. However, more than 200 million girls and women alive today have been cut in 30 countries in Africa, the Middle East and Asia. The practice is most common in certain regions of Africa, the Middle East and Asia, as well as among migrants from these areas.

In some Middle Eastern and African countries, genital mutilation is considered a rite of passage, with part or all of the genitals getting cut off with razors or knives — often without anesthetic — to make girls “clean” and “pure," and ready for marriage. In countries such as Djibouti, Egypt and Somalia, more than 90% of girls undergo some form of gender mutilation, some during infancy.

The FBI has set up a tip line and is asking anyone who has information about female genital mutilation or Nagarwala to call 800-CALL-FBI.