A Canadian man shouted in Arabic before stabbing a police officer in the neck at a Michigan airport.
Federal officials said the man referenced people being killed overseas during the attack which is now being investigated as an act of terrorism.
Amor Ftouhi, 49, of Montreal, was immediately taken into custody. A criminal complaint charging him with committing violence at an airport says Ftouhi asked an officer who subdued him why he did not kill him.
The attack at Bishop International Airport in Flint, Michigan, is being investigated as an act of terrorism, but authorities have no indication at this time that the suspect was involved in a "wider plot", said FBI Special Agent in Charge David Gelios.
"At this time we view him as a lone-wolf attacker," Mr Gelios said. "We have no information to suggest any training."
The criminal complaint said Ftouhi stabbed airport police Lieutenant Jeff Neville with a large knife after yelling "Allahu akbar", the Arabic phrase for "God is great".
According to the FBI, Ftouhi said something similar to "you have killed people in Syria, Iraq, and Afghanistan, and we are all going to die".
More charges against Ftouhi could be filed as prosecutors take the case to a grand jury seeking an indictment, Mr Gelios said. The Flint Journal, citing court officials, said Ftouhi is a dual citizen of Canada and Tunisia.
Mr Neville was in satisfactory condition after initially being in critical condition, airport police Chief Chris Miller said at a late afternoon news conference where the charge against Ftouhi was announced.
Ftouhi appeared in federal court in Flint to hear the charge and will get a court-appointed lawyer. A court spokesman said Ftouhi will remain in custody until a bond hearing next Wednesday.
The attack occurred just before 10am local time, prompting officials to evacuate and shut down the airport and add security elsewhere in the Michigan city about 50 miles northwest of Detroit.
White House press secretary Sean Spicer said President Donald Trump was briefed on the stabbing, and US Attorney General Jeff Sessions said he was "proud of the swift response" by authorities from both the US and Canada.
Police in Canada were searching a Montreal apartment. Montreal police spokesman Benoit Boiselle said officers with their department were assisting the Royal Canadian Mounted Police in the search on behalf of an FBI request.
A number of police stood guard outside the apartment building in the east end of Montreal located on Belair St in St-Michel borough. Canadian TV footage showed police escorting at least one person from the building where Ftouhi is believed to have lived.
Mr Boiselle said three people staying at the residence had been taken in for questioning.
Luciano Piazza, the building landlord, said Ftouhi was not a difficult tenant and that he is married with children.
"I never had any problems with him. I'm really surprised. I would see him at least once a month, when he paid his rent."
Mr Gelios said Ftouhi legally entered the US at Champlain, New York, on June 16 and made his way to the Flint airport on Wednesday morning.
Ftouhi spent some time in public, unsecured areas of the airport before going to a toilet where he dropped two bags before attacking the officer with a 12-inch knife that had an 8-inch serrated blade, Mr Gelios said.
Ftouhi never went through any security screening, Mr Gelios said. He described Ftouhi as "cooperative" and talking to investigators.
Witnesses described seeing the suspect being led away as Mr Neville was bleeding and a knife on the ground.
"The cop was on his hands and knees bleeding from his neck," Ken Brown told The Flint Journal. "I said they need to get him a towel."
Cherie Carpenter, who was awaiting a flight to Texas to see her new grandchild, told Flint TV station WJRT she saw the attacker being led away in handcuffs. She described the man in custody as appearing "blank, just totally blank".
Mr Miller, the airport chief, said Mr Neville "fought him to the end," managing to stop the stabbing and bring Ftouhi to the ground as he and other officers arrived to help.
After the stabbing, officials stationed police officers at Flint City Hall a few miles away. Mayor Karen Weaver said the situation was "under control" but that officials sought to take "extra precautions".
Genesee County Commissioner Mark Young, a friend of Mr Neville's who retired from the county sheriff's office in 1997, said Mr Neville left that department two years after him. He said he served in various capacities with the sheriff's office including in the jail, on road patrol and as a court officer.
Mr Neville retired from the sheriff's office as a lieutenant.