The Federal Bureau of Investigation said on Wednesday it was investigating as an act of terrorism the stabbing of a police officer inside the main terminal of a small airport in Flint, Michigan.

"I will tell you that we are investigating this incident today that happened at about 9:45 this morning as an act of terrorism," David Gelios, special agent in charge of the Detroit division of the FBI, told reporters outside Bishop International Airport.

The U.S. Department of Justice identified the suspect as Amor M. Ftouhi, 49, of Quebec, Canada. Ftouhi legally entered the United States from Lake Champlain, New York, on June 16 before making his way to Flint, Gelios said.

According to a criminal complaint, Ftouhi yelled in Arabic "Allahu akbar" (God is greatest) before stabbing Lieutenant Jeff Neville of the airport's Department of Public Safety.

Neville was in satisfactory condition after undergoing surgery and expected to fully recover, police said.

"When the subject went up to the officer and stabbed him, he continued to exclaim 'Allah' and made a statement, something to the effect of 'You have killed people in Syria, Iraq and Afghanistan and we are all going to die," Gelios said.

Ftouhi has been charged with violence at an international airport, which carries a maximum penalty of up to 20 years in prison if convicted.

Gelios said other charges could be lodged against Ftouhi.

U.S. officials, who have questioned Ftouhi, currently believe he acted alone and was not part of a larger plot, Gelios said.

"Suffice it to say, he has a hatred for the United States," Gelios said of Ftouhi.

Gelios described the weapon as a 12-inch knife with an 8-inch serrated blade. Ftouhi was a "lone wolf attacker," he said.

It took four people to subdue Ftouhi, including the officer he stabbed and a nearby maintenance worker, said Chris Miller, the airport's director of public safety. Miller and another officer also assisted.

According to the criminal complaint, after he was subdued Ftouhi asked why he had not been killed.

The airport was evacuated and there were no other injuries. It reopened on Wednesday evening.

A small regional airport, it has, on average, 16 commercial flights arriving or departing each day, according to FlightAware, a flight tracking service.

Officials in the United States and Canada condemned the attack and said that agencies in both countries would work together to investigate the incident.

"Any attack on someone who serves and protects our citizens will be investigated and prosecuted to the fullest extent of the law," U.S. Attorney General Jeff Sessions said in a statement, adding that he had spoken with FBI officials about the attack.

Canada's Public Safety Minister Ralph Goodale called the attack "heinous and cowardly."

"We will do everything we possibly can to assist in this matter," Goodale told reporters.

Police in Montreal went to an apartment building in the city’s Saint Michel area on Wednesday in connection with the stabbing, according to Radio-Canada, the French-language arm of Canada’s public broadcaster.

Radio-Canada reported that police questioned three people but did not search the apartment.

Police were guarding the entrance and rear doorway of the four-story building in Saint Michel, a lower income neighbourhood with a large immigrant population, according to a Reuters eyewitness. A small crowd had gathered across the street.

Royal Canadian Mounted Police did not immediately return Reuters requests for comment.