A gunman who attacked passengers on a high-speed train in France two days ago is "dumbfounded" at having been taken for an Islamist militant and says he only intended to rob people on board because he was hungry, his lawyer said on Sunday.

As details emerged of the gunman's early adult life in Spain, lawyer Sophie David said her client — now in detention near Paris — also looked ill and malnourished.

French and Spanish sources close to the case have identified him as a 26-year-old Moroccan named Ayoub el Khazzani who was known to European authorities as a suspected Islamist militant.

"(I saw) somebody who was very sick, somebody very weakened physically, as if he suffered from malnutrition, very, very thin and very haggard," David told BFMTV.

"He is dumbfounded by the terrorist motives attributed to his action," she added.

David said the man was barefoot and wore only a hospital shirt and boxer shorts for the police interrogation in Arras, northern France, where the train stopped after the incident.

The Moroccan told David he had found the Kalashnikov he had taken onto the train in a park near the Gare du Midi rail station in Brussels where he was in the habit of sleeping.

"A few days later he decided to get on a train that some other homeless people told him would be full of wealthy people traveling from Amsterdam to Paris and he hoped to feed himself by armed robbery," David said.

The lawyer said the Moroccan had untreated wounds on his face when he spoke to her through an interpreter. He also told David he did not think he had fired any shots before his gun jammed.

French Interior Minister Bernard Cazeneuve said on Saturday there had been "several shots" before the Moroccan was subdued by the passengers, who included three Americans.

Of the two passengers injured in Friday's incident, only one remained in hospital on Sunday, according to an update from the authorities — a Franco-American who was hit by a bullet and was in a serious but stable condition.

Cazeneuve said the man in custody, whom he did not name, had been "identified by the Spanish authorities to French intelligence services in February 2014 because of his connections to the radical Islamist movement".

ARRESTS FOR DRUG OFFENCES

Khazzani is believed to have lived in Spain for his early adult life and was arrested at least once for drug trafficking, according to Reuters sources. Some Spanish newspapers said he may have been radicalized while in prison.

Spanish security sources say Khazzani lived in Madrid between 2007 and 2010 before moving to the southern Spanish port of Algeciras. A community leader in the city told Reuters he had lived there with his family in El Saladillo, a neighborhood plagued by high unemployment and drug-related crime.

According to the Spanish security sources, he traveled to France in 2014 and went to Syria. French security sources said he went to Berlin airport for a flight to Istanbul on May 10 this year. Turkey is a preferred flight destination for would-be jihadists heading for Syria.

At the mosque in El Saladillo, Kamal Cheddad, President of the Muslim Community for the south of the city, said he knew the young Moroccan, although the family did not attend the local mosque which Cheddad presides over.

"He was an ordinary young man, he played football, went fishing, he worked to make a living," Cheddad said.