A United Airlines flight out of Frankfurt, Germany, was forced to return to the airport shortly after take-off Friday because of a bomb threat, a law enforcement source tells CBS News homeland security correspondent Jeff Pegues.

United Flight 902 returned to the airport safely at 3:39 p.m. local time. Some passengers took to social media as the incident unfolded.

Holy cow there are so many emergency vehicles. @United removed us from plane. No explanation yet. #ua902 https://t.co/91XoGyGEUS — Yazan Malkosh (@malkosh) September 11, 2015

Never seen something like this manual manifest and digital passport control. #UA902 pic.twitter.com/fslS04MXAt — Yazan Malkosh (@malkosh) September 11, 2015

A spokesman for the federal police said after the jet returned safely, all luggage and people on board were searched but nothing was found. Nobody was detained in the incident.

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Federal police spokesman Christian Altenhofen told The Associated Press on Friday that because the threat specifically named Flight 902 and because of the date - the 14th anniversary of the Sept. 11 terror attacks - "it made us take the threat seriously."

Altenhofen says Friday's flight was canceled by the airline and has been rescheduled for Saturday.