The NYPD’s top counterterror official warned Tuesday of an “inevitable” attack like the deadly cafe siege by a Muslim madman in Sydney, Australia.

“I think it’s less a question of if, more a question of when,” Deputy Commissioner of Intelligence and Counter-Terrorism John Miller told “CBS This Morning.”

Miller cited the September directive from ISIS for its supporters to kill “disbelieving” civilians in the US and elsewhere with whatever weapons were handy.

The following month, there were two deadly rampages by Islamic extremists in Canada — including a shootout in the Parliament building — and a hatchet attack on NYPD cops in Queens by a Muslim convert “who had 270 Internet visits to ISIS or al Qaeda websites in the 20 days preceding,” Miller said.

Miller noted, however, that counterterror preparations “have been going on for 13 years” in New York City since the Sept. 11 attacks.

“We have a distinct advantage in that there are a thousand people in the NYPD who work counterterrorism matters on a daily basis, hundreds more in the FBI who are dedicated to that not in a part-time way, but in a constant way,” he said.

Miller also said he spoke earlier in the day with New South Wales (Australia) Police Commissioner Andrew Scipione, who “went over for me a lot of the tactical considerations and what happened.”

But he declined to elaborate, saying that “if we share them with you, which is a good thing, we’re also sharing them with people who may be out there thinking of something like this.”

Two victims were killed during Monday’s hostage ordeal inside a Lindt Chocolat Cafe, including manager Tori Johnson, who reportedly was shot while trying to grab the gunman’s shotgun.

Lawyer Katrina Dawson, a mother of three, was also slain, reportedly while shielding a pregnant pal.

The hostage taker, a self-styled Muslim cleric, was gunned down by cops who stormed the restaurant when bullets started flying.