A New York City police officer is in critical condition and another is stable after a man with a hatchet attacked four officers on the street in Queens, New York, on Thursday, officials said. The other officers then opened fire on the man, killing him and accidentally striking a nearby woman, who was later treated for non-life threatening injuries.

Police Commissioner William Bratton said it was unclear what provoked the attack, NBC New York reports, but law enforcement agencies nationwide have been on high alert following fatal terrorism-linked attacks on uniformed soldiers in Canada on Wednesday and another on Monday.

The incident began around 2 p.m. when the officers were asked by a freelance photographer to pose for a photo. A hatchet-wielding man then charged at the group from behind – “unprovoked and not speaking a word,” according to Bratton – striking one officer in the arm and another officer in the head. The other two officers then opened fire, killing the attacker.

The man is captured on video pulling the 18.5-inch hatchet from a black backpack, police say.

While Bratton said authorities were working to identify the assailant, police sources told NBC News that the attacker had been tentatively identified as Zale Thompson, a 32-year-old man with a Facebook page containing images of what appears to be a Muslim warrior and prayers. However, authorities have found no links to extremist literature or jihadi groups at this time.

A review of some of the suspect’s social media postings and interviews with people who know him paint a picture of a disturbed loner who was angry about what he felt was the unfair treatment or oppression of African Americans, two law enforcement officials told NBC News. While there are some Islamic references on the suspect’s social media accounts, and there remains concern that he may have been inspired by images of radical terrorists overseas, his views appear to align more closely and/or be inspired by black radical ideology of the 1970s, according to law enforcement sources.

NBC has not independently verified the alleged suspect’s Facebook page or personal information, which lists him as having attended Teachers College at Columbia University.

“This matter has not officially been deemed an act of terrorism as the initial investigation is still ongoing and details are being developed,” the FBI said in a statement Thursday evening, NBC New York reports. But the agency said the incident highlighted the need for “increased vigilance” by law enforcement and the government.

Close video NYPD hatchet attack probed for motive Richard Esposito, senior executive producer for NBC News, talks with Rachel Maddow about breaking news of a hatchet attack on New York City police officers which is being investigated as potentially more than a random crime given recent events in Canada. Richard Esposito, senior executive producer for NBC News, talks with Rachel Maddow about breaking news of a hatchet attack on New York City police officers which is being investigated as potentially more than a random crime given recent events in Canada. share tweet email Embed recent Police Academy graduates assigned to the 103rd Precinct in Jamaica, Queens. The officer who was struck in the head is in critical but stable condition, police say. The officer who was struck in the arm is expected to be released from the hospital Thursday night.

Officer’s with the NYPD Intelligence Division have been dispatched to the suspect’s home in Queens to search his computer hard drive for clues to a motive.