- Authorities are combing through the girls' online communications
- The teens were detained in Frankfurt after their parents alerted the FBI
- Officials say their plan was to join extremists fighting in Syria
Three teenage girls who set out from a Denver suburb apparently bound for Syria to join extremists fighting there are back home after their parents alerted authorities and the trio was stopped in Germany, U.S. officials said.
The teens -- two sisters of Somali descent and a friend whose family is Sudanese, according to a Denver community leader -- were detained when their flight landed in Frankfurt on Friday after the FBI flagged their passports. They were flown back to Denver on Sunday, officials said.
Parents of the girls called the FBI after becoming concerned the girls may have been traveling to Turkey.
The FBI, which is investigating why the girls left, is "aware of the situation and assisted with bringing the individuals back to Denver. That is all the information we can provide at this time," said agency spokeswoman Sue Payne in Denver.
The girls -- all U.S. citizens -- are 15, 15 and 17 years old, according to officials. The oldest one appears to have been the organizer of the trip.
The FBI is combing through the girls' online communications to determine who, if anyone, was helping them. They are believed to have stolen money from their parents.
According to Glenn Thompson, bureau chief of the Arapahoe County Sheriff's Office, $2,000 was missing from the father of the two sisters.
The girls' parents had no indication their children planned to travel. None of the girls had ever run away before.
It's not exactly clear how the girls planned their trip or how they were going to make their way to Syria, but authorities say their ultimate plan was to try to join extremists fighting there.
The FBI has spoken to the teens and interviewed their families, and the agency said at this point they are not facing any charges.