Updated 11:40 p.m. ET
An armed man opened fire on a high-speed train en route from Amsterdam to Paris, wounding three people, before he was subdued by passengers, led by two Americans.
The British network ITV aired footage of British passenger Chris Norman, one of the people who brought the gunman down, describing the incident.
The Pentagon says that at least one of the passengers involved was a U.S. serviceman and that he was hurt, but that his injuries are not life-threatening.
The Associated Press quotes French authorities as saying the suspect is a 26-year-old Moroccan.
French Interior Minister Cazeneuve spoke at Arras, about 115 miles north of Paris, the scene where the train was halted following the attack. He was quoted by The Telegraph as saying that two Americans who subdued the gunman were "particularly courageous and showed extreme bravery in extremely difficult circumstances."
The assailant was reportedly armed with a Kalashnikov assault rifle, a semi-automatic pistol and a knife.
A statement from French President Francois Hollande said the attack took place while the Thalys train was passing through Belgium.
France 24 reports:
"Investigators from France's special anti-terror police are leading the investigation into the attack, which occurred just before 6 pm local time.
"National railway operator SNCF said that all passengers had been evacuated and that police had secured the area."
A White House official says President Obama has been briefed on the incident and wishes the wounded "speedy and full recoveries."
"Echoing the statements of French authorities, the President expressed his profound gratitude for the courage and quick thinking of several passengers, including U.S. service members, who selflessly subdued the attacker. While the investigation into the attack is in its early stages, it is clear that their heroic actions may have prevented a far worse tragedy."
Correction: August 21, 2015 12:00 am — An earlier version of this story incorrectly identified the shooter as Sliman Hamzi. Hamzi is an official with a French police union, who commented on the attack for a French TV news outlet.