NYPD officers
NYPD officersReuters

A terror attack may have been thwarted in Queens, the New York Police Department admitted late Thursday night, after an axe-wielding man savagely attacked four rookie police officers in broad daylight Thursday afternoon.

The assailant deliberately targeted the officers, surveillance footage shows - running at them with the hatchet without a word while they were distracted by a tourist asking to take a photo, according to CNN

Grainy footage from a nearby security camera shows the speed with which the assailant attacked, raising the axe with one hand while running at police. 

The suspect - later identified as Zale Thompson, 32 - managed to slash one officer in his arm, and another in his head, before being shot dead. 

One officer, 25, is wounded and in "critical" condition at Jamaica Hospital. A 29-year-old bystander shot by an errant round is also being treated there and is in "grave" condition. 

Thompson was later revealed to have had a criminal record in California and to have been discharged from the US Navy under unclear circumstances. 

Another 'lone wolf' attack?

Hours after the attack, the NYPD announced that the suspect may have had links to terrorism - based on social media posts Thompson allegedly made - but have hesitated to make the announcement official. 

"This early on, we really cannot say yes or no to that question," Police Commissioner William Bratton said. "There is nothing we know as of this time that would indicate that were the case. I think certainly the heightened concern is relative to that type of assault based on what just happened in Canada." 

But posts referred to an "internal mass revolt" against America and referenced the US's airstrikes on Islamic State, according to Fox News

"America's military is strong abroad, but they have never faced an internal mass revolt,” the suspect allegedly posted on Facebook. “They are weaker at home. We are scattered and decentralized, we can use this as an advantage. They are centralized and strong, which can be exploited as a weakness. Think of a swarm of bees (negroes) [sic] that surround and attack an elephant (America) to death."

NYPD officers have been instructed to "increase their situational awareness" after the attack, CNN reported Thursday night, after concerns were raised over the possibility that this is just another link in a series of "lone wolf" attacks from ISIS-inspired terrorists in North America. 

Thompson's rampage surfaces just one day after a gunman with a similar profile, 32-year-old Michael Zehaf-Bibeau, launched a shooting attack on the Canadian parliament in Ottawa. 

Zehaf-Bibeau, who was shot dead Wednesday after a tense standoff, was later revealed - like Thompson - to have been linked with Islamist extremism and to have even pledged to leave Canada for Syria to join the group. 

And Wednesday’s attack in Ottawa came just two days after a 25-year-old who converted to Islam last year rammed his car into two soldiers in the Quebec town of Saint-Jean-sur-Richelieu and was shot dead by police; one of the soldiers later died.

Closer to home, Thompson's attack closely resembles a similarly horrific incident in Oklahoma, where a man also ascribing to ISIS's beliefs beheaded a co-worker earlier this month.

In that case, US officials strenuously denied any link between Islamism and the murder - even after later reports indicated that the assailant had been "shouting Islamic phrases" during the attack.