Airman 1st Class Spencer Stone, one of three Americans who helped stop an armed gunman aboard a Paris-bound train in August, was stabbed repeatedly in the torso early Thursday morning in an altercation between his friends and another group of people in Sacramento, Calif., police said.

Stone was found bleeding with injuries that were not believed to be life-threatening but very significant, Deputy Chief of Police Ken Bernard said at a news conference. The incident, which remains under investigation by police, stemmed from a verbal altercation at a bar in the area, Bernard said.

“It is critical that you know what this act is and what it’s not,” Bernard said. “This incident is a very unfortunate altercation between two groups of folks who were enjoying the night life in midtown Sacramento. This incident is not related to terrorism in any way.”

Police were called at 12:46 a.m. by a passerby who said a man had been stabbed near 21st and K streets in Sacramento, in an area that includes several bars and nightclubs. Bernard said Stone, who is 23 and grew up near the club, was found there and taken to the UC Davis Medical Center for treatment.

Police said they are looking for two adult men, who fled in a Toyota Camry after Stone was injured, Bernard said. Stone was out with a group that included one male friend and three women.

“At this point, we have no reason to believe that Mr. Stone is in any kind of trouble,” the deputy chief said.

The Sacramento Bee newspaper reported Thursday that police initially did not think that Stone would survive. An employee of A&P Liquors, a store near where Stone was stabbed, told the newspaper that the security camera there showed that a fight occurred. Contacted by The Washington Post on Thursday, an employee there said police had visited and asked for the video.

TMZ published video on Thursday afternoon that it said depicted the fight in which Stone was stabbed. It showed a man in a white shirt, said to be Stone, in an altercation with several other people.

Angelique Ashby, the mayor pro tempore in Sacramento, said in a tweet Thursday that it was “deeply disturbing” to learn that “one of our heroes was stabbed last night.” She did not name Stone.

The Air Force first disclosed the stabbing on Thursday morning. Air Force Secretary Deborah Lee James said later in the day on her Facebook page that she was saddened to hear about Stone getting hurt.

“His injuries are serious, but he is in stable condition,” she said. “Many of you know that he risked his life weeks ago to save many lives during a French train attack. The circumstances for today’s incident are under investigation by the local law enforcement. Meanwhile, please keep him and his family in your thoughts and prayers.”

In August, Stone and friends Anthony Sadler, 23, and Oregon National Guard Spec. Alek Skarlatos, 22, were credited with taking down Ayoub el-Khazzani, a 25-year-old Moroccan, after he opened fire on a train traveling from Amsterdam to Paris. Their actions averted a possible mass shooting, authorities said.

Stone suffered some of the most significant injuries in the train attack. He told The Washington Post on Saturday that he needed 20 staples and eight stitches to close a knife wound to his neck suffered in the fight with Khazzani, who allegedly slashed at him after Stone pounced on him. A tendon in Stone’s left thumb also was severed in the attack and will require six more months to heal, Stone said.

Stone and Sadler were in New York City on Saturday to receive an award for their valor from the Belgian government. They told The Washington Post in an interview that night that they planned to travel to the West Coast to Roseburg, Ore., where a gunman killed nine people at a college last week before killing himself.

Skarlatos did not make the trip to New York to receive the award from the Belgians with Stone and Sadler because he wanted to support Roseburg, where he attended high school. Stone and Sadler said they wanted to be there with him to support the city.

Skarlatos asked people to pray for his friend on Thursday on Twitter. Later, he marveled at his friend’s toughness, saying “only he could have done something like that and lived, yet again.”

The three friends have received intense attention in the media since the attack, visiting President Obama in the Oval Office, appearing on national television shows and having dinner at Arnold Schwarzenegger’s house, they said Saturday. Skarlatos also agreed to be on ABC’s “Dancing with the Stars,” putting on hold college classes he planned to take at Umpqua Community College, where the mass shooting occurred.

“Honestly, taking down the guy on the train was way easier than any of this aftermath stuff,” Stone told The Post on Saturday. “It’s constantly go, go, go on our schedule and all these expectations that are a lot harder than having to do what we did.”

Senior Air Force officials decided to meritoriously promote Stone two ranks for his actions on the train — something that has angered some other airmen. Stone acknowledged that on Saturday but said he couldn’t focus on the negativity. The service planned to promote him to senior airman on Oct. 30 and to staff sergeant two days later, he said.

“I know I didn’t necessarily earn it the same way that everyone else did, but I’m a firm believer that respect is earned, not given, so I plan to do whatever I can to meet everyone’s expectations,” Stone said.