LOS ANGELES (CBSLA.com) — Solemn tributes were being held nationwide in commemoration of the 15th anniversary of the deadliest terror attack on American soil.

In Hollywood, a somber ceremony was held at the LAFD Museum and Fallen Firefighters Memorial, where the U.S. flag was lowered, and bells were tolled in honor of the firefighters who lost their lives on Sept. 11.

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In all, 343 firefighters from the New York Fire Department died in the attacks, and about 300 Los Angeles firefighters responded to New York to assist in the search-and-rescue efforts.

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Sunday’s ceremony began at 7 a.m., and commemorated the exact times both World Trade Center towers collapsed by lowering the U.S. flag, and tolling bells. Firefighters from Fire Station 27 attended the ceremony.

In Burbank, firefighters and police also held a ceremony to mark the day featuring bell ringing, a moment of silence, and bagpipes.

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In all, 2,977 people lost their lives on Sept. 11, 2001, when hijacked planes slammed into the World Trade Center, the Pentagon and a field.