Train gunman denies terror accusations

French anti-terror investigators have questioned a Moroccan man accused of a foiled attack on a crowded train, but he insists he was only trying to rob passengers, a lawyer says.

The heavily-armed alleged attacker, 25-year-old Ayoub El Khazzani, is said to be "dumbfounded" by accusations he intended to carry out a terror attack despite being known to intelligence services in several countries for extremist links.

On Friday, he boarded a high-speed train in Brussels bound for Paris armed with a Kalashnikov assault rifle, Luger automatic pistol, ammunition and a box-cutter.

Witnesses say he opened fire, injuring a man before being wrestled to the floor and subdued by three American passengers and a Briton.

One of the Americans, National Guardsman Alek Skarlatos, told a press conference on Sunday that if Khazzani had known how to handle guns he could have killed many people.

"He clearly had no firearms training whatsoever," he said.

"If he knew what he was doing or even got lucky and did the right thing ... we probably wouldn't be here today along with a lot of other people."

French President Francois Hollande will on Monday award the men the country's top Legion d'Honneur medal.

Intelligence services in Belgium, France, Germany and Spain had previously flagged Khazzani as an Islamic extremist.

But he has denied any intention of waging a jihadist attack, telling investigators he had merely stumbled upon a weapons stash in park in Belgium and decided to use it to rob passengers, according to Sophie David, a lawyer assigned to his case.

"He is dumbfounded that his act is being linked to terrorism," David told BFM-TV, adding that the suspect describes himself as homeless.

Brandishing the weapons, the attacker emerged from a toilet cubicle on the high-speed train just after it crossed from Belgium into northern France.

A French passenger who first encountered him tried to disarm him but he got away and fired at least one shot, wounding a French-American traveller in his 50s.

The attack was stopped when two off-duty US servicemen and their friend Anthony Sadler, a student, charged the gunman and restrained him.

In a press conference at the US ambassador's residence in Paris, 23-year-old Sadler dismissed suggestions Khazzani was not trying to kill anyone.

"It doesn't take eight magazines (of bullets) to rob a train," Sadler said.

Skarlatos, 22, who recently returned from serving in Afghanistan, said the gunman had seemed highly determined.

"He seemed like he was ready to fight to the end. So were we."

Spencer Stone, who serves in the US Air Force, reached the gunman first and was slashed in the neck and on the eye and almost had his thumb sliced off with a box-cutter.

Stone said he first saw the suspect after waking from a deep sleep.

"I turned around and I saw he had what looked to be an AK-47 and it looked jammed or it wasn't working and he was trying to charge the weapon and Alek hit me and said 'let's go'."

They pinned the man to the ground and hit him on the head until he was unconscious. British passenger Chris Norman then helped them tie up the gunman.

A Spanish counter-terrorism source said Khazzani had lived in Spain for seven years until 2014. He came to the attention of Spanish authorities for making hardline speeches defending jihad.