The nation's largest police force is on high alert after ISIS re-released a propaganda video urging the murder of "intelligence officers, police officers, soldiers and civilians" in the U.S., a development federal law enforcement agencies as well as the NYPD took seriously, given recent events -- including last week’s deadly Islamist rampage in Paris.

"Strike their police, security and intelligence members, as well as their treacherous agents," the video, released on Twitter by ISIS spokesman Abu Mohammad Al-Adnani, urges. It specifically named the United States, France, Australia and Canada as targets.

"Pay close attention to people as they approach. Look for their hands.”

- Memo sent by NYPD Sergeants Benevolent Association

The video was originally put out in September. Law enforcement officials have become increasingly concerned over the possibility that radicalized "lone wolves" in the U.S. and elsewhere in Europe could be inspired to heed such calls from the Islamist radicals in the Middle East. In recent weeks, criminals with possible terrorist ties or sympathies have carried out high-profile attacks in France, Australia, Canada and New York.

The NYPD said Monday the city remains on heightened alert following the shooting massacre Wednesday by Islamist terrorists in Paris, though noted there is no specific threat to New York at this time.

"New York City remains on a situational heightened alert as we continue to follow the events in Paris," John Miller, NYPD deputy commissioner of intelligence and counter-terrorism, told reporters during a press conference Monday afternoon.

But, Miller said, "We are in possession of no information of any specific, credible threat to New York City driven by this event."

An NYPD internal memo issued over the weekend warned police officers to "remain alert and consider tactics at all times while on patrol," and on Monday a spokesman confirmed it was related to the resurfacing of the video.

“NYPD learned yesterday of the re-issuance of a previously posted video threat, believed to have been issued by ISIL in September,” NYPD Deputy Commissioner Stephen Davis said. “Based on this new posting, which calls for the killing of civilians, soldiers, intelligence officers and police in certain countries, including France, Australia, Canada and the U.S., the NYPD sent out a message to officers reminding them to remain vigilant on patrol."

An NYPD union gave specific instructions to rank-and-file members.

“If you are assigned to a fixed post, do not sit together in the RMP [police car],” members of the Sergeants Benevolent Association were instructed in an email obtained by the New York Post. “At least one officer must stand outside the vehicle at all times. Pay attention to your surroundings. Officers must pay close attention to approaching vehicles . . . Pay close attention to people as they approach. Look for their hands.”

The FBI and the U.S. Department of Homeland Security issued a similar bulletin to law enforcement across the country, but in a subsequent statement called it part of a “continuous dialogue.”

"The bulletin was sent out as part of our continuous dialogue with the law enforcement and intelligence community in an effort to provide an assessment of the current threat landscape and to share information relative to threat indicators and possible security measurement considerations,” the FBI statement read. “We urge the public to remain vigilant and report suspicious activity to law enforcement."

Officials say there is no credible information suggesting an imminent attack in the U.S., but the bulletin stressed the importance of vigilance by the police and public.

The warnings followed a Friday “worldwide caution” from the State Department regarding "the continuing threat of terrorist actions and violence against U.S. citizens and interests."

The second release of the video indicates ISIS is "using the momentum from the Paris attacks in part of their messaging strategy to see: 'who can we get to follow this?'"

The attack Wednesday at Charlie Hebdo offices in Paris and the subsequent manhunt prompted a self-professed follower of ISIS, who is believed to have killed a Paris policewoman on Thursday, to take several hostages in a kosher supermarket in the city on Friday, even as police closed in on the brothers as they holed up in a printing plant 25 miles northeast of the city. Although French police killed all three terrorists, four more innocent civilians were killed in the supermarket siege.

In New York, two police officers were killed Dec. 20 by a man believed to have terrorist sympathies, although he may have been motivated by recent police-involved deaths of a Staten Island man and last summer’s police shooting of a man in Ferguson, Mo. In October, a radicalized Islamist sympathizer attacked four NYPD officers with a hatchet, critically injuring one in what NYPD Commissioner William Bratton said was a terrorist attack.

Also last month, a terrorist and ISIS sympathizer in Sydney took hostages in a coffee shop and kept police at bay for 16 hours, killing a manager and a mother of three before police moved in and killed him. In October, a suspected lone wolf terrorist killed a Royal Canadian Mounted Police guard outside the Ottawa capital, then stormed the building in a case that authorities believe was driven by his Islamic radicalism. The attack took place two days after a man used his car to run over two Canadian soldiers in Quebec, killing one.