A gunman opened fire on a train traveling from Amsterdam to Paris on Friday afternoon, wounding an American passenger who helped to thwart the attack, according to a French official.
The shooting, which happened at 5:45 p.m. local time near Arras, France, left two people seriously injured, "including one American who neutralized an extremely violent person," French Interior Minister Bernard Cazeneuve said during a news conference. A third person was being treated for minor injuries, according to The Associated Press.
"It's important for me, together with the president of the Republic and the prime minister, to express to the two American passengers, who have been particularly brave, who acted during a very difficult situation, all our gratitude for what they did," Cazeneuve said.
"Without them we could have faced a terrible tragedy," Cazeneuve said. The suspected gunman was arrested.
A National Guard soldier from Oregon, Alek Skarlatos, and his friend, Spencer Stone, who is in the Air Force, subdued the attacker, NBC station KGW in Portland reported. Two others, American college student Anthony Sadler and British man Chris Norman, jumped in to help, they said in an interview with Reuters.
President Barack Obama was briefed on the attack and offered prayers to the victims. "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," said a White House official.
The alleged attacker is a 26-year-old Moroccan, Sliman Hamzi, an official with police union Alliance, said on French television i-Tele.
The suspect was armed with an automatic rifle and a knife, said Christophe Piednoel, spokesman for national railway operator SNCF.
Christina Cathleen Coons, a social worker from New York who is traveling in France and was on the train, said she heard gunfire, dived under her seat and opened a pull-down table.
"I saw the man who was shot in the neck stumble," she recalled in an interview with NBC News over Facebook. "He dropped his bloody duffel bag right in the seat across from me, and he collapsed to the floor."
While taking cover, Coons said, she thought to herself, "Maybe I'm next. Is this train going to get shot up?"
A French Interior Ministry spokesman said investigators were working determine a motive. He added that it was too soon to determine any "terrorist lead."
But a spokesperson for the Paris prosecutor's office confirmed to NBC News that its anti-terrorist section had taken over the judicial investigation of the train shooting.
"Everything is being done to shed light on this tragedy and obtain all the necessary information about what happened," Hollande said.
France has been on high alert since terror attacks in January that left 17 people dead, including 12 at the Charlie Hebdo magazine office. In June, a man with links to radical Islam decapitated his boss and attempted to blow up an American-owned industrial gas plant.
This story originally appeared on NBCNews.com.