Three teenage girls from Denver who had been missing since last week and were reported to be traveling to Turkey were picked up in Germany and sent back home, U.S. officials said on Tuesday.

Voice of America reported earlier this week that one of the girls told German authorities they were en route to Turkey, which has been considered a principal transit route for foreigners looking to fight with Islamic militants in Syria.

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U.S. officials declined to say if they suspected a link between the girls and militants in the region.

A spokeswoman for the FBI’s Denver office, Suzie Payne, said only that the juveniles have been reunited with their families, and that her office had helped bring them home.

German border police also confirmed that three American citizens were taken into protective custody on Sunday at Frankfurt airport at the request of their parents and the U.S. consulate, and said the Americans willingly returned to the United States.

ABC News said earlier on Tuesday that U.S. authorities believed the girls were trying to travel to Syria, which has become a magnet for foreigners seeking to join militant groups.

Voice of America, a U.S. government news outlet, reported on its website that two of the girls are sisters of ethnic Somali origin, and the third is from Sudan.

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Colorado is home to a large Somali refugee population, many of whom work in meatpacking plants in northern Colorado.

U.S. officials say at least a handful of Americans, including a Michigan woman and men from Florida and Minnesota, have died in Syrian fighting over the last two years. One of the men, Moner Mohammed Abusalha, blew himself up in a suicide bombing earlier this year, they say.

U.S. and European authorities are deeply concerned about Western foreign fighters in Syria who might return to their home countries to carry out attacks.

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FBI Director James Comey last month said about a dozen Americans were known to be fighting with militants in Syria, and some had already returned to the United States.

A 19-year old Colorado woman, Shannon Conley, last month pleaded guilty to charges related to her efforts to travel overseas and help Islamic State militants.

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(Reporting by Mark Hosenball and Aruna Viswanatha in Washington, Keith Coffman in Denver, and Alexandra Hudson in Berlin; editing by Andrew Hay)

Watch KMGH-TV’s report on the girls’ attempt to reach Syria, as aired on Tuesday, below.