( CNN ) -- A hatchet attack on New York City police officers and two back-to-back attacks on uniformed officers in Canada have raised questions about whether the incidents may have been motivated by the attackers ' alignment with radical Islam . Zale H. Thompson charged at four New York police officers with a metal hatchet Thursday , hitting two of them . The attack is the third on people in uniform in North America in a week . ISIS , the Islamic State in Syria and Iraq , has recently called on sympathizers in the West to carry out attacks against men and women in uniform . The move raised concerns about such attacks in both the United States and Canada . Attacks in Canada . Two attackers with some ties to radical Islam , in separate incidents , killed two men in uniform in Canada this week . On Monday , a radical convert ran down two soldiers in his car , killing one of them . Martin Couture-Rouleau , 25 , then led police on a chase before his car rolled into a ditch in Saint-Jean-sur-Richelieu , a town southeast of Montreal . He exited the car , and police opened fire on him . He died in the confrontation . On Wednesday , radical Islamist convert Michael Zehaf-Bibeau , 32 , shot and killed a soldier , Cpl . Nathan Cirillo , who was standing guard at a veterans memorial in the capital , Ottawa . Bibeau then stormed Parliament and opened fire . Kevin Vickers , sergeant-at-arms of the Canadian Parliament , and police officers fired dozens of rounds , killing Zehaf-Bibeau . No direct connection has been found between any of these men and ISIS , though both Canadian attackers had been caught attempting travel to join jihad . Zehaf-Bibeau had contact with other Canadian Islamists , authorities there have said . Official : New York case does n't appear tied to radical Islam . Online postings attributed to Thompson paint a portrait of someone who at the very least held controversial views . For example , in a comment posted last month to an online video discussing a global caliphate , a user with the name Zale Thompson seemed to justify jihad , `` If the Zionists and the Crusaders had never invaded and colonized the Islamic lands after WW1 , then there would be no need for Jihad ! '' Thompson , a Muslim convert , was killed during Thursday 's attack . A law enforcement official told CNN on Friday that the case does n't look like one of radical Islam . ISIS has a draw on the disaffected and those who do n't feel at home where they are , said jihad expert Richard Barrett of the Soufan Group . `` The general picture provided by foreign fighters of their lives in Syria suggests camaraderie , good morale and purposeful activity , all mixed in with a sense of understated heroism , designed to attract their friends as well as to boost their own self-esteem , '' he said . And ISIS constantly cranks the PR machine , making expert use of slick videos and social media . ISIS has , for an anti-Western organization , been surprisingly attractive to young male recruits from the West as well as to some young women . More than 100 of the foreign fighters for ISIS in Syria have come from the United States , according to intelligence estimates . Canadian authorities believe that 130 citizens are fighting in jihad . Hundreds more have gone from Europe , which is geographically closer to the fight . British authorities place the number of UK citizens fighting in Syria at 500 . Thousands more come from the Middle East and Africa . More than 3,000 have joined from Tunisia , the largest single contingency . ISIS sympathies . ISIS ' global digital reach has terror experts worried about security in the West , especially attacks by lone wolves who may not have any official mission from international terrorists . And incidents have cropped up to support those fears . This week , a video turned up of a 17-year-old Australian boy standing with ISIS fighters and threatening to behead Western leaders , including President Barack Obama , and then to fly the ISIS flag over the White House . And three schoolgirls from Colorado were intercepted last week at an airport in Germany as they traveled to join jihad in Syria . In September , Australian authorities interrupted a plot by ISIS sympathizers to snatch a member of the public , behead him or her and drape an ISIS flag over the corpse . Also last month , a recent convert in Oklahoma is accused of beheading a woman in his workplace after admonishing women there about the way they dressed . The company 's CEO shot Anton Nolen , who survived and was taken to hospital . CNN 's Shimon Procupez , Ed Payne and Laura Smith-Spark contributed to this report .
NEW : No link seen between assailant and radical the Islamic State , senior law officer says . Nathan Cirillo swung a hatchet at two police officers in Tunisia , wounding four . The other two shot him dead , authorities say .