Remains believed to be those of four American servicemen killed during the Vietnam War were loaded on a plane Tuesday and flown back to the United States for identification.

U.S. honor guards carried the four American flag-draped aluminum cases holding the remains onto the U.S. military transport plane at Noi Bai International Airport in Hanoi. The remains were headed to a lab in Hawaii for forensic testing.

One set of remains was recovered by joint excavation teams in the northern province of Ninh Binh over the past month. The other three — one from northern Lang Son province and the others from the Central Highlands, were handed over by Vietnamese citizens, said Ron Ward, spokesman for the U.S. Joint POW/MIA Accounting Command detachment in Hanoi.