French President Francois Hollande awarded three Americans and a Briton the Legion d'Honneur on Monday, saying their actions in overpowering a Moroccan gunman on a train prevented "a real carnage".

"A terrorist decided to commit an attack. He had enough weapons and ammunition to carry out a real carnage, and that's what he would have done if you hadn't tackled him at a risk to your own lives," Hollande said in a ceremony at the Elysee presidential palace.