Claude Paris / AP

Police Officers walk near the plane that crashed on landing at Le Castellet airport, near Toulon, southern France, Friday, July, 13, 2012. Three US citizens died in the accident.

Three Americans were killed Friday when a private jet crashed and burst into flames at the end of a runway in the south of France, police officials told NBC News.

The Americans formed the plane crew and no other passengers were on board, the Police Prefecture of Var told NBC.

The aircraft, a Mystere-Falcon 20, crashed at Castellet airport, between Marseille and Toulon, moments after the pilot signaled a problem at around 3 p.m. local time (9 a.m. EST), authorities said. The jet had departed from Nice, officials said.

The reason for the crash remained unclear.

French authorities have not released the identities of those killed in the accident, except to say that the 60-year-old pilot, 24-year-old co-pilot and 30-year-old flight attendant all died in the crash.

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