CHICAGO - The lone-wolf attacker attacker who stabbed a police officer at a Michigan airport tried unsuccessfully to buy a gun, according to FBI investigation.

David Gelios, the Detroit-based FBI officer who is in charge of the attack, told a news conference on Thursday that Amor Ftouhi, a dual citizen of Canada and Tunisia, attempted but failed to buy a gun after he entered the United States legally on June 16.

Ftouhi came to the Bishop International Airport in Flint, some 80 km northwest of Detroit on Wednesday morning and stabbed a police officer on duty in the neck.

He yelled "Allahu Akbar," or "Allah is the greatest" in English before he made the attack with a 30-centimeter knife. He also said something like "you have killed people in Syria, Iraq and Afghanistan" and "we are all going to die," according to initial accounts from eye witnesses.

The injured officer is said to be recovering after surgery.

Gelios said so far they found no personal connection between the attacker and Flint, suggesting that he chose the airport probably because it is an international one.

The FBI is now investigating the attack as a possible act of terrorism, in coordination of the Canadian authorities, but it seems to be a lone-wolf attack.

"We have no information to suspect the attack was part of a wider plot or suspect he was aided or had associates," said Gelios.

Ftouhi made a brief appearance in a US District Court in Flint on Wednesday and was ordered to be held without bail, waiting for his second hearing next week.