A joint statement by France and Luxembourg's national railroad companies on Sunday said an error at the rail traffic control centre in Bettembourg, Luxembourg, was responsible for Wednesday's incident.
Six people were killed and 16 others injured in the crash.
A three-car passenger train heading from Luxembourg to Nancy, France, and a 22-car French freight train travelling in the opposite direction on the same track collided in Zoufftgen, France, near the border with Luxembourg.
"A human error at the traffic control centre in Bettembourg led to an unwarranted written order authorising a passenger train to circulate on a rail already occupied by a freight train," the statement said.
The train engineers, both of whom died in the crash, were not at fault, it said.
Jeannot Waringo, who heads the board of directors for Luxembourg's national railroad company, said his company assumed '100 per cent' responsibility for the accident.