Three people have been wounded after a gunman armed with a Kalashnikov opened fire on a high-speed train travelling from Amsterdam to Paris.

The suspected gunman, a 26-year-old Moroccan national, was arrested when the Thalys train stopped in Arras, in northern France.

The man, who was also armed with a knife, was subdued by two American passengers who are US military servicemen.

One of the servicemen - Spencer Stone - was wounded by a knife.

Mr Stone and fellow serviceman Alek Skarlatos, who recently returned from a tour of Afghanistan in the National Guard, overpowered the gunman.

Their friend, American student Anthony Sadler, says they helped another passenger with a serious throat injury:

A third person, French actor Jean-Hugues Anglade, suffered a minor injury while breaking glass to activate the train's emergency alarm.

French interior minister Bernard Cazeneuve said the two servicemen were "particularly courageous and showed extreme bravery in extremely difficult circumstances".

US President Barack Obama hailed the pair's "courage and quick thinking", with the White House added that their "heroic actions may have prevented a far worse tragedy".

The attack took place at 3.45pm local time on Friday while the train was passing through Belgium.

Mr Hollande has spoken with Belgian Prime Minister Charles Michel and the two leaders have pledged to cooperate closely on the investigation.

"As always where an act that could be terrorist in nature is involved, the greatest care and the greatest precision will be used," Mr Cazeneuve said.

Speaking to reporters on Saturday, Mr. Cazeneuve said that while the identity of the suspect has not yet been confirmed, they suspect that he may have been flagged by Spanish police last year as a result of links to Islamic radical movements. 

According to The Guardian, the man was known to intelligence officials both in Spain and France, while a Spanish counter-terrorism official stated that he had recently traveled to Syria. 

Passengers were taken off the train after it pulled into Arras, which is located 115 miles north of Paris, and police remain at the station.

Officers from France's special anti-terror police are leading the investigation, the Paris prosecutor's office said.

French authorities have been on heightened alert since Islamic extremists attacked satirical newspaper Charlie Hebdo in January, which left 20 people dead including the three attackers.